/*
 * Copyright (C) 2001-2004 by David Brownell
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/* this file is part of ehci-hcd.c */

/*-------------------------------------------------------------------------*/

/*
 * EHCI hardware queue manipulation ... the core.  QH/QTD manipulation.
 *
 * Control, bulk, and interrupt traffic all use "qh" lists.  They list "qtd"
 * entries describing USB transactions, max 16-20kB/entry (with 4kB-aligned
 * buffers needed for the larger number).  We use one QH per endpoint, queue
 * multiple urbs (all three types) per endpoint.  URBs may need several qtds.
 *
 * ISO traffic uses "ISO TD" (itd, and sitd) records, and (along with
 * interrupts) needs careful scheduling.  Performance improvements can be
 * an ongoing challenge.  That's in "ehci-sched.c".
 *
 * USB 1.1 devices are handled (a) by "companion" OHCI or UHCI root hubs,
 * or otherwise through transaction translators (TTs) in USB 2.0 hubs using
 * (b) special fields in qh entries or (c) split iso entries.  TTs will
 * buffer low/full speed data so the host collects it at high speed.
 */

/*-------------------------------------------------------------------------*/

/* fill a qtd, returning how much of the buffer we were able to queue up */

static int
qtd_fill(struct ehci_hcd *ehci, struct ehci_qtd *qtd, dma_addr_t buf,
                  size_t len, int token, int maxpacket)
{
        int     i, count;
        u64     addr = buf;

        /* one buffer entry per 4K ... first might be short or unaligned */
        qtd->hw_buf[0] = cpu_to_hc32(ehci, (u32)addr);
        qtd->hw_buf_hi[0] = cpu_to_hc32(ehci, (u32)(addr >> 32));
        count = 0x1000 - (buf & 0x0fff);        /* rest of that page */
        if (likely (len < count))               /* ... iff needed */
                count = len;
        else {
                buf +=  0x1000;
                buf &= ~0x0fff;

                /* per-qtd limit: from 16K to 20K (best alignment) */
                for (i = 1; count < len && i < 5; i++) {
                        addr = buf;
                        qtd->hw_buf[i] = cpu_to_hc32(ehci, (u32)addr);
                        qtd->hw_buf_hi[i] = cpu_to_hc32(ehci,
                                        (u32)(addr >> 32));
                        buf += 0x1000;
                        if ((count + 0x1000) < len)
                                count += 0x1000;
                        else
                                count = len;
                }

                /* short packets may only terminate transfers */
                if (count != len)
                        count -= (count % maxpacket);
        }
        qtd->hw_token = cpu_to_hc32(ehci, (count << 16) | token);
        qtd->length = count;

        return count;
}

/*-------------------------------------------------------------------------*/

static inline void
qh_update (struct ehci_hcd *ehci, struct ehci_qh *qh, struct ehci_qtd *qtd)
{
        struct ehci_qh_hw *hw = qh->hw;

        /* writes to an active overlay are unsafe */
        BUG_ON(qh->qh_state != QH_STATE_IDLE);

        hw->hw_qtd_next = QTD_NEXT(ehci, qtd->qtd_dma);
        hw->hw_alt_next = EHCI_LIST_END(ehci);

        /* Except for control endpoints, we make hardware maintain data
         * toggle (like OHCI) ... here (re)initialize the toggle in the QH,
         * and set the pseudo-toggle in udev. Only usb_clear_halt() will
         * ever clear it.
         */
        if (!(hw->hw_info1 & cpu_to_hc32(ehci, 1 << 14))) {
                unsigned        is_out, epnum;

                is_out = !(qtd->hw_token & cpu_to_hc32(ehci, 1 << 8));
                epnum = (hc32_to_cpup(ehci, &hw->hw_info1) >> 8) & 0x0f;
                if (unlikely (!usb_gettoggle (qh->dev, epnum, is_out))) {
                        hw->hw_token &= ~cpu_to_hc32(ehci, QTD_TOGGLE);
                        usb_settoggle (qh->dev, epnum, is_out, 1);
                }
        }

        /* HC must see latest qtd and qh data before we clear ACTIVE+HALT */
        wmb ();
        hw->hw_token &= cpu_to_hc32(ehci, QTD_TOGGLE | QTD_STS_PING);
}

/* if it weren't for a common silicon quirk (writing the dummy into the qh
 * overlay, so qh->hw_token wrongly becomes inactive/halted), only fault
 * recovery (including urb dequeue) would need software changes to a QH...
 */
static void
qh_refresh (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        struct ehci_qtd *qtd;

        if (list_empty (&qh->qtd_list))
                qtd = qh->dummy;
        else {
                qtd = list_entry (qh->qtd_list.next,
                                struct ehci_qtd, qtd_list);
                /* first qtd may already be partially processed */
                if (cpu_to_hc32(ehci, qtd->qtd_dma) == qh->hw->hw_current)
                        qtd = NULL;
        }

        if (qtd)
                qh_update (ehci, qh, qtd);
}

/*-------------------------------------------------------------------------*/

static void qh_link_async(struct ehci_hcd *ehci, struct ehci_qh *qh);

static void ehci_clear_tt_buffer_complete(struct usb_hcd *hcd,
                struct usb_host_endpoint *ep)
{
        struct ehci_hcd         *ehci = hcd_to_ehci(hcd);
        struct ehci_qh          *qh = ep->hcpriv;
        unsigned long           flags;

        spin_lock_irqsave(&ehci->lock, flags);
        qh->clearing_tt = 0;
        if (qh->qh_state == QH_STATE_IDLE && !list_empty(&qh->qtd_list)
                        && HC_IS_RUNNING(hcd->state))
                qh_link_async(ehci, qh);
        spin_unlock_irqrestore(&ehci->lock, flags);
}

static void ehci_clear_tt_buffer(struct ehci_hcd *ehci, struct ehci_qh *qh,
                struct urb *urb, u32 token)
{

        /* If an async split transaction gets an error or is unlinked,
         * the TT buffer may be left in an indeterminate state.  We
         * have to clear the TT buffer.
         *
         * Note: this routine is never called for Isochronous transfers.
         */
        if (urb->dev->tt && !usb_pipeint(urb->pipe) && !qh->clearing_tt) {
#ifdef DEBUG
                struct usb_device *tt = urb->dev->tt->hub;
                dev_dbg(&tt->dev,
                        "clear tt buffer port %d, a%d ep%d t%08x\n",
                        urb->dev->ttport, urb->dev->devnum,
                        usb_pipeendpoint(urb->pipe), token);
#endif /* DEBUG */
                if (!ehci_is_TDI(ehci)
                                || urb->dev->tt->hub !=
                                   ehci_to_hcd(ehci)->self.root_hub) {
                        if (usb_hub_clear_tt_buffer(urb) == 0)
                                qh->clearing_tt = 1;
                } else {

                        /* REVISIT ARC-derived cores don't clear the root
                         * hub TT buffer in this way...
                         */
                }
        }
}

static int qtd_copy_status (
        struct ehci_hcd *ehci,
        struct urb *urb,
        size_t length,
        u32 token
)
{
        int     status = -EINPROGRESS;

        /* count IN/OUT bytes, not SETUP (even short packets) */
        if (likely (QTD_PID (token) != 2))
                urb->actual_length += length - QTD_LENGTH (token);

        /* don't modify error codes */
        if (unlikely(urb->unlinked))
                return status;

        /* force cleanup after short read; not always an error */
        if (unlikely (IS_SHORT_READ (token)))
                status = -EREMOTEIO;

        /* serious "can't proceed" faults reported by the hardware */
        if (token & QTD_STS_HALT) {
                if (token & QTD_STS_BABBLE) {
                        /* FIXME "must" disable babbling device's port too */
                        status = -EOVERFLOW;
                /* CERR nonzero + halt --> stall */
                } else if (QTD_CERR(token)) {
                        status = -EPIPE;

                /* In theory, more than one of the following bits can be set
                 * since they are sticky and the transaction is retried.
                 * Which to test first is rather arbitrary.
                 */
                } else if (token & QTD_STS_MMF) {
                        /* fs/ls interrupt xfer missed the complete-split */
                        status = -EPROTO;
                } else if (token & QTD_STS_DBE) {
                        status = (QTD_PID (token) == 1) /* IN ? */
                                ? -ENOSR  /* hc couldn't read data */
                                : -ECOMM; /* hc couldn't write data */
                } else if (token & QTD_STS_XACT) {
                        /* timeout, bad CRC, wrong PID, etc */
                        ehci_dbg(ehci, "devpath %s ep%d%s 3strikes\n",
                                urb->dev->devpath,
                                usb_pipeendpoint(urb->pipe),
                                usb_pipein(urb->pipe) ? "in" : "out");
                        status = -EPROTO;
                } else {        /* unknown */
                        status = -EPROTO;
                }

                ehci_vdbg (ehci,
                        "dev%d ep%d%s qtd token %08x --> status %d\n",
                        usb_pipedevice (urb->pipe),
                        usb_pipeendpoint (urb->pipe),
                        usb_pipein (urb->pipe) ? "in" : "out",
                        token, status);
        }

        return status;
}

static void
ehci_urb_done(struct ehci_hcd *ehci, struct urb *urb, int status)
__releases(ehci->lock)
__acquires(ehci->lock)
{
        if (likely (urb->hcpriv != NULL)) {
                struct ehci_qh  *qh = (struct ehci_qh *) urb->hcpriv;

                /* S-mask in a QH means it's an interrupt urb */
                if ((qh->hw->hw_info2 & cpu_to_hc32(ehci, QH_SMASK)) != 0) {

                        /* ... update hc-wide periodic stats (for usbfs) */
                        ehci_to_hcd(ehci)->self.bandwidth_int_reqs--;
                }
                qh_put (qh);
        }

        if (unlikely(urb->unlinked)) {
                COUNT(ehci->stats.unlink);
        } else {
                /* report non-error and short read status as zero */
                if (status == -EINPROGRESS || status == -EREMOTEIO)
                        status = 0;
                COUNT(ehci->stats.complete);
        }

#ifdef EHCI_URB_TRACE
        ehci_dbg (ehci,
                "%s %s urb %p ep%d%s status %d len %d/%d\n",
                __func__, urb->dev->devpath, urb,
                usb_pipeendpoint (urb->pipe),
                usb_pipein (urb->pipe) ? "in" : "out",
                status,
                urb->actual_length, urb->transfer_buffer_length);
#endif

        /* complete() can reenter this HCD */
        usb_hcd_unlink_urb_from_ep(ehci_to_hcd(ehci), urb);
        spin_unlock (&ehci->lock);
        usb_hcd_giveback_urb(ehci_to_hcd(ehci), urb, status);
        spin_lock (&ehci->lock);
}

static void start_unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh);
static void unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh);

static int qh_schedule (struct ehci_hcd *ehci, struct ehci_qh *qh);

/*
 * Process and free completed qtds for a qh, returning URBs to drivers.
 * Chases up to qh->hw_current.  Returns number of completions called,
 * indicating how much "real" work we did.
 */
static unsigned
qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        struct ehci_qtd         *last, *end = qh->dummy;
        struct list_head        *entry, *tmp;
        int                     last_status;
        int                     stopped;
        unsigned                count = 0;
        u8                      state;
        const __le32            halt = HALT_BIT(ehci);
        struct ehci_qh_hw       *hw = qh->hw;

        if (unlikely (list_empty (&qh->qtd_list)))
                return count;

        /* completions (or tasks on other cpus) must never clobber HALT
         * till we've gone through and cleaned everything up, even when
         * they add urbs to this qh's queue or mark them for unlinking.
         *
         * NOTE:  unlinking expects to be done in queue order.
         *
         * It's a bug for qh->qh_state to be anything other than
         * QH_STATE_IDLE, unless our caller is scan_async() or
         * scan_periodic().
         */
        state = qh->qh_state;
        qh->qh_state = QH_STATE_COMPLETING;
        stopped = (state == QH_STATE_IDLE);

 rescan:
        last = NULL;
        last_status = -EINPROGRESS;
        qh->needs_rescan = 0;

        /* remove de-activated QTDs from front of queue.
         * after faults (including short reads), cleanup this urb
         * then let the queue advance.
         * if queue is stopped, handles unlinks.
         */
        list_for_each_safe (entry, tmp, &qh->qtd_list) {
                struct ehci_qtd *qtd;
                struct urb      *urb;
                u32             token = 0;

                qtd = list_entry (entry, struct ehci_qtd, qtd_list);
                urb = qtd->urb;

                /* clean up any state from previous QTD ...*/
                if (last) {
                        if (likely (last->urb != urb)) {
                                ehci_urb_done(ehci, last->urb, last_status);
                                count++;
                                last_status = -EINPROGRESS;
                        }
                        ehci_qtd_free (ehci, last);
                        last = NULL;
                }

                /* ignore urbs submitted during completions we reported */
                if (qtd == end)
                        break;

                /* hardware copies qtd out of qh overlay */
                rmb ();
                token = hc32_to_cpu(ehci, qtd->hw_token);

                /* always clean up qtds the hc de-activated */
 retry_xacterr:
                if ((token & QTD_STS_ACTIVE) == 0) {

                        /* on STALL, error, and short reads this urb must
                         * complete and all its qtds must be recycled.
                         */
                        if ((token & QTD_STS_HALT) != 0) {

                                /* retry transaction errors until we
                                 * reach the software xacterr limit
                                 */
                                if ((token & QTD_STS_XACT) &&
                                                QTD_CERR(token) == 0 &&
                                                ++qh->xacterrs < QH_XACTERR_MAX &&
                                                !urb->unlinked) {
                                        ehci_dbg(ehci,
        "detected XactErr len %zu/%zu retry %d\n",
        qtd->length - QTD_LENGTH(token), qtd->length, qh->xacterrs);

                                        /* reset the token in the qtd and the
                                         * qh overlay (which still contains
                                         * the qtd) so that we pick up from
                                         * where we left off
                                         */
                                        token &= ~QTD_STS_HALT;
                                        token |= QTD_STS_ACTIVE |
                                                        (EHCI_TUNE_CERR << 10);
                                        qtd->hw_token = cpu_to_hc32(ehci,
                                                        token);
                                        wmb();
                                        hw->hw_token = cpu_to_hc32(ehci,
                                                        token);
                                        goto retry_xacterr;
                                }
                                stopped = 1;

                        /* magic dummy for some short reads; qh won't advance.
                         * that silicon quirk can kick in with this dummy too.
                         *
                         * other short reads won't stop the queue, including
                         * control transfers (status stage handles that) or
                         * most other single-qtd reads ... the queue stops if
                         * URB_SHORT_NOT_OK was set so the driver submitting
                         * the urbs could clean it up.
                         */
                        } else if (IS_SHORT_READ (token)
                                        && !(qtd->hw_alt_next
                                                & EHCI_LIST_END(ehci))) {
                                stopped = 1;
                                goto halt;
                        }

                /* stop scanning when we reach qtds the hc is using */
                } else if (likely (!stopped
                                && HC_IS_RUNNING (ehci_to_hcd(ehci)->state))) {
                        break;

                /* scan the whole queue for unlinks whenever it stops */
                } else {
                        stopped = 1;

                        /* cancel everything if we halt, suspend, etc */
                        if (!HC_IS_RUNNING(ehci_to_hcd(ehci)->state))
                                last_status = -ESHUTDOWN;

                        /* this qtd is active; skip it unless a previous qtd
                         * for its urb faulted, or its urb was canceled.
                         */
                        else if (last_status == -EINPROGRESS && !urb->unlinked)
                                continue;

                        /* qh unlinked; token in overlay may be most current */
                        if (state == QH_STATE_IDLE
                                        && cpu_to_hc32(ehci, qtd->qtd_dma)
                                                == hw->hw_current) {
                                token = hc32_to_cpu(ehci, hw->hw_token);

                                /* An unlink may leave an incomplete
                                 * async transaction in the TT buffer.
                                 * We have to clear it.
                                 */
                                ehci_clear_tt_buffer(ehci, qh, urb, token);
                        }

                        /* force halt for unlinked or blocked qh, so we'll
                         * patch the qh later and so that completions can't
                         * activate it while we "know" it's stopped.
                         */
                        if ((halt & hw->hw_token) == 0) {
halt:
                                hw->hw_token |= halt;
                                wmb ();
                        }
                }

                /* unless we already know the urb's status, collect qtd status
                 * and update count of bytes transferred.  in common short read
                 * cases with only one data qtd (including control transfers),
                 * queue processing won't halt.  but with two or more qtds (for
                 * example, with a 32 KB transfer), when the first qtd gets a
                 * short read the second must be removed by hand.
                 */
                if (last_status == -EINPROGRESS) {
                        last_status = qtd_copy_status(ehci, urb,
                                        qtd->length, token);
                        if (last_status == -EREMOTEIO
                                        && (qtd->hw_alt_next
                                                & EHCI_LIST_END(ehci)))
                                last_status = -EINPROGRESS;

                        /* As part of low/full-speed endpoint-halt processing
                         * we must clear the TT buffer (11.17.5).
                         */
                        if (unlikely(last_status != -EINPROGRESS &&
                                        last_status != -EREMOTEIO)) {
                                /* The TT's in some hubs malfunction when they
                                 * receive this request following a STALL (they
                                 * stop sending isochronous packets).  Since a
                                 * STALL can't leave the TT buffer in a busy
                                 * state (if you believe Figures 11-48 - 11-51
                                 * in the USB 2.0 spec), we won't clear the TT
                                 * buffer in this case.  Strictly speaking this
                                 * is a violation of the spec.
                                 */
                                if (last_status != -EPIPE)
                                        ehci_clear_tt_buffer(ehci, qh, urb,
                                                        token);
                        }
                }

                /* if we're removing something not at the queue head,
                 * patch the hardware queue pointer.
                 */
                if (stopped && qtd->qtd_list.prev != &qh->qtd_list) {
                        last = list_entry (qtd->qtd_list.prev,
                                        struct ehci_qtd, qtd_list);
                        last->hw_next = qtd->hw_next;
                }

                /* remove qtd; it's recycled after possible urb completion */
                list_del (&qtd->qtd_list);
                last = qtd;

                /* reinit the xacterr counter for the next qtd */
                qh->xacterrs = 0;
        }

        /* last urb's completion might still need calling */
        if (likely (last != NULL)) {
                ehci_urb_done(ehci, last->urb, last_status);
                count++;
                ehci_qtd_free (ehci, last);
        }

        /* Do we need to rescan for URBs dequeued during a giveback? */
        if (unlikely(qh->needs_rescan)) {
                /* If the QH is already unlinked, do the rescan now. */
                if (state == QH_STATE_IDLE)
                        goto rescan;

                /* Otherwise we have to wait until the QH is fully unlinked.
                 * Our caller will start an unlink if qh->needs_rescan is
                 * set.  But if an unlink has already started, nothing needs
                 * to be done.
                 */
                if (state != QH_STATE_LINKED)
                        qh->needs_rescan = 0;
        }

        /* restore original state; caller must unlink or relink */
        qh->qh_state = state;

        /* be sure the hardware's done with the qh before refreshing
         * it after fault cleanup, or recovering from silicon wrongly
         * overlaying the dummy qtd (which reduces DMA chatter).
         */
        if (stopped != 0 || hw->hw_qtd_next == EHCI_LIST_END(ehci)) {
                switch (state) {
                case QH_STATE_IDLE:
                        qh_refresh(ehci, qh);
                        break;
                case QH_STATE_LINKED:
                        /* We won't refresh a QH that's linked (after the HC
                         * stopped the queue).  That avoids a race:
                         *  - HC reads first part of QH;
                         *  - CPU updates that first part and the token;
                         *  - HC reads rest of that QH, including token
                         * Result:  HC gets an inconsistent image, and then
                         * DMAs to/from the wrong memory (corrupting it).
                         *
                         * That should be rare for interrupt transfers,
                         * except maybe high bandwidth ...
                         */

                        /* Tell the caller to start an unlink */
                        qh->needs_rescan = 1;
                        break;
                /* otherwise, unlink already started */
                }
        }

        return count;
}

/*-------------------------------------------------------------------------*/

// high bandwidth multiplier, as encoded in highspeed endpoint descriptors
#define hb_mult(wMaxPacketSize) (1 + (((wMaxPacketSize) >> 11) & 0x03))
// ... and packet size, for any kind of endpoint descriptor
#define max_packet(wMaxPacketSize) ((wMaxPacketSize) & 0x07ff)

/*
 * reverse of qh_urb_transaction:  free a list of TDs.
 * used for cleanup after errors, before HC sees an URB's TDs.
 */
static void qtd_list_free (
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        struct list_head        *qtd_list
) {
        struct list_head        *entry, *temp;

        list_for_each_safe (entry, temp, qtd_list) {
                struct ehci_qtd *qtd;

                qtd = list_entry (entry, struct ehci_qtd, qtd_list);
                list_del (&qtd->qtd_list);
                ehci_qtd_free (ehci, qtd);
        }
}

/*
 * create a list of filled qtds for this URB; won't link into qh.
 */
static struct list_head *
qh_urb_transaction (
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        struct list_head        *head,
        gfp_t                   flags
) {
        struct ehci_qtd         *qtd, *qtd_prev;
        dma_addr_t              buf;
        int                     len, maxpacket;
        int                     is_input;
        u32                     token;

        /*
         * URBs map to sequences of QTDs:  one logical transaction
         */
        qtd = ehci_qtd_alloc (ehci, flags);
        if (unlikely (!qtd))
                return NULL;
        list_add_tail (&qtd->qtd_list, head);
        qtd->urb = urb;

        token = QTD_STS_ACTIVE;
        token |= (EHCI_TUNE_CERR << 10);
        /* for split transactions, SplitXState initialized to zero */

        len = urb->transfer_buffer_length;
        is_input = usb_pipein (urb->pipe);
        if (usb_pipecontrol (urb->pipe)) {
                /* SETUP pid */
                qtd_fill(ehci, qtd, urb->setup_dma,
                                sizeof (struct usb_ctrlrequest),
                                token | (2 /* "setup" */ << 8), 8);

                /* ... and always at least one more pid */
                token ^= QTD_TOGGLE;
                qtd_prev = qtd;
                qtd = ehci_qtd_alloc (ehci, flags);
                if (unlikely (!qtd))
                        goto cleanup;
                qtd->urb = urb;
                qtd_prev->hw_next = QTD_NEXT(ehci, qtd->qtd_dma);
                list_add_tail (&qtd->qtd_list, head);

                /* for zero length DATA stages, STATUS is always IN */
                if (len == 0)
                        token |= (1 /* "in" */ << 8);
        }

        /*
         * data transfer stage:  buffer setup
         */
        buf = urb->transfer_dma;

        if (is_input)
                token |= (1 /* "in" */ << 8);
        /* else it's already initted to "out" pid (0 << 8) */

        maxpacket = max_packet(usb_maxpacket(urb->dev, urb->pipe, !is_input));

        /*
         * buffer gets wrapped in one or more qtds;
         * last one may be "short" (including zero len)
         * and may serve as a control status ack
         */
        for (;;) {
                int this_qtd_len;

                this_qtd_len = qtd_fill(ehci, qtd, buf, len, token, maxpacket);
                len -= this_qtd_len;
                buf += this_qtd_len;

                /*
                 * short reads advance to a "magic" dummy instead of the next
                 * qtd ... that forces the queue to stop, for manual cleanup.
                 * (this will usually be overridden later.)
                 */
                if (is_input)
                        qtd->hw_alt_next = ehci->async->hw->hw_alt_next;

                /* qh makes control packets use qtd toggle; maybe switch it */
                if ((maxpacket & (this_qtd_len + (maxpacket - 1))) == 0)
                        token ^= QTD_TOGGLE;

                if (likely (len <= 0))
                        break;

                qtd_prev = qtd;
                qtd = ehci_qtd_alloc (ehci, flags);
                if (unlikely (!qtd))
                        goto cleanup;
                qtd->urb = urb;
                qtd_prev->hw_next = QTD_NEXT(ehci, qtd->qtd_dma);
                list_add_tail (&qtd->qtd_list, head);
        }

        /*
         * unless the caller requires manual cleanup after short reads,
         * have the alt_next mechanism keep the queue running after the
         * last data qtd (the only one, for control and most other cases).
         */
        if (likely ((urb->transfer_flags & URB_SHORT_NOT_OK) == 0
                                || usb_pipecontrol (urb->pipe)))
                qtd->hw_alt_next = EHCI_LIST_END(ehci);

        /*
         * control requests may need a terminating data "status" ack;
         * bulk ones may need a terminating short packet (zero length).
         */
        if (likely (urb->transfer_buffer_length != 0)) {
                int     one_more = 0;

                if (usb_pipecontrol (urb->pipe)) {
                        one_more = 1;
                        token ^= 0x0100;        /* "in" <--> "out"  */
                        token |= QTD_TOGGLE;    /* force DATA1 */
                } else if (usb_pipebulk (urb->pipe)
                                && (urb->transfer_flags & URB_ZERO_PACKET)
                                && !(urb->transfer_buffer_length % maxpacket)) {
                        one_more = 1;
                }
                if (one_more) {
                        qtd_prev = qtd;
                        qtd = ehci_qtd_alloc (ehci, flags);
                        if (unlikely (!qtd))
                                goto cleanup;
                        qtd->urb = urb;
                        qtd_prev->hw_next = QTD_NEXT(ehci, qtd->qtd_dma);
                        list_add_tail (&qtd->qtd_list, head);

                        /* never any data in such packets */
                        qtd_fill(ehci, qtd, 0, 0, token, 0);
                }
        }

        /* by default, enable interrupt on urb completion */
        if (likely (!(urb->transfer_flags & URB_NO_INTERRUPT)))
                qtd->hw_token |= cpu_to_hc32(ehci, QTD_IOC);
        return head;

cleanup:
        qtd_list_free (ehci, urb, head);
        return NULL;
}

/*-------------------------------------------------------------------------*/

// Would be best to create all qh's from config descriptors,
// when each interface/altsetting is established.  Unlink
// any previous qh and cancel its urbs first; endpoints are
// implicitly reset then (data toggle too).
// That'd mean updating how usbcore talks to HCDs. (2.7?)


/*
 * Each QH holds a qtd list; a QH is used for everything except iso.
 *
 * For interrupt urbs, the scheduler must set the microframe scheduling
 * mask(s) each time the QH gets scheduled.  For highspeed, that's
 * just one microframe in the s-mask.  For split interrupt transactions
 * there are additional complications: c-mask, maybe FSTNs.
 */
static struct ehci_qh *
qh_make (
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        gfp_t                   flags
) {
        struct ehci_qh          *qh = ehci_qh_alloc (ehci, flags);
        u32                     info1 = 0, info2 = 0;
        int                     is_input, type;
        int                     maxp = 0;
        struct usb_tt           *tt = urb->dev->tt;
        struct ehci_qh_hw       *hw;

        if (!qh)
                return qh;

        /*
         * init endpoint/device data for this QH
         */
        info1 |= usb_pipeendpoint (urb->pipe) << 8;
        info1 |= usb_pipedevice (urb->pipe) << 0;

        is_input = usb_pipein (urb->pipe);
        type = usb_pipetype (urb->pipe);
        maxp = usb_maxpacket (urb->dev, urb->pipe, !is_input);

        /* 1024 byte maxpacket is a hardware ceiling.  High bandwidth
         * acts like up to 3KB, but is built from smaller packets.
         */
        if (max_packet(maxp) > 1024) {
                ehci_dbg(ehci, "bogus qh maxpacket %d\n", max_packet(maxp));
                goto done;
        }

        /* Compute interrupt scheduling parameters just once, and save.
         * - allowing for high bandwidth, how many nsec/uframe are used?
         * - split transactions need a second CSPLIT uframe; same question
         * - splits also need a schedule gap (for full/low speed I/O)
         * - qh has a polling interval
         *
         * For control/bulk requests, the HC or TT handles these.
         */
        if (type == PIPE_INTERRUPT) {
                qh->usecs = NS_TO_US(usb_calc_bus_time(USB_SPEED_HIGH,
                                is_input, 0,
                                hb_mult(maxp) * max_packet(maxp)));
                qh->start = NO_FRAME;

                if (urb->dev->speed == USB_SPEED_HIGH) {
                        qh->c_usecs = 0;
                        qh->gap_uf = 0;

                        qh->period = urb->interval >> 3;
                        if (qh->period == 0 && urb->interval != 1) {
                                /* NOTE interval 2 or 4 uframes could work.
                                 * But interval 1 scheduling is simpler, and
                                 * includes high bandwidth.
                                 */
                                dbg ("intr period %d uframes, NYET!",
                                                urb->interval);
                                goto done;
                        }
                } else {
                        int             think_time;

                        /* gap is f(FS/LS transfer times) */
                        qh->gap_uf = 1 + usb_calc_bus_time (urb->dev->speed,
                                        is_input, 0, maxp) / (125 * 1000);

                        /* FIXME this just approximates SPLIT/CSPLIT times */
                        if (is_input) {         // SPLIT, gap, CSPLIT+DATA
                                qh->c_usecs = qh->usecs + HS_USECS (0);
                                qh->usecs = HS_USECS (1);
                        } else {                // SPLIT+DATA, gap, CSPLIT
                                qh->usecs += HS_USECS (1);
                                qh->c_usecs = HS_USECS (0);
                        }

                        think_time = tt ? tt->think_time : 0;
                        qh->tt_usecs = NS_TO_US (think_time +
                                        usb_calc_bus_time (urb->dev->speed,
                                        is_input, 0, max_packet (maxp)));
                        qh->period = urb->interval;
                }
        }

        /* support for tt scheduling, and access to toggles */
        qh->dev = urb->dev;

        /* using TT? */
        switch (urb->dev->speed) {
        case USB_SPEED_LOW:
                info1 |= (1 << 12);     /* EPS "low" */
                /* FALL THROUGH */

        case USB_SPEED_FULL:
                /* EPS 0 means "full" */
                if (type != PIPE_INTERRUPT)
                        info1 |= (EHCI_TUNE_RL_TT << 28);
                if (type == PIPE_CONTROL) {
                        info1 |= (1 << 27);     /* for TT */
                        info1 |= 1 << 14;       /* toggle from qtd */
                }
                info1 |= maxp << 16;

                info2 |= (EHCI_TUNE_MULT_TT << 30);

                /* Some Freescale processors have an erratum in which the
                 * port number in the queue head was 0..N-1 instead of 1..N.
                 */
                if (ehci_has_fsl_portno_bug(ehci))
                        info2 |= (urb->dev->ttport-1) << 23;
                else
                        info2 |= urb->dev->ttport << 23;

                /* set the address of the TT; for TDI's integrated
                 * root hub tt, leave it zeroed.
                 */
                if (tt && tt->hub != ehci_to_hcd(ehci)->self.root_hub)
                        info2 |= tt->hub->devnum << 16;

                /* NOTE:  if (PIPE_INTERRUPT) { scheduler sets c-mask } */

                break;

        case USB_SPEED_HIGH:            /* no TT involved */
                info1 |= (2 << 12);     /* EPS "high" */
                if (type == PIPE_CONTROL) {
                        info1 |= (EHCI_TUNE_RL_HS << 28);
                        info1 |= 64 << 16;      /* usb2 fixed maxpacket */
                        info1 |= 1 << 14;       /* toggle from qtd */
                        info2 |= (EHCI_TUNE_MULT_HS << 30);
                } else if (type == PIPE_BULK) {
                        info1 |= (EHCI_TUNE_RL_HS << 28);
                        /* The USB spec says that high speed bulk endpoints
                         * always use 512 byte maxpacket.  But some device
                         * vendors decided to ignore that, and MSFT is happy
                         * to help them do so.  So now people expect to use
                         * such nonconformant devices with Linux too; sigh.
                         */
                        info1 |= max_packet(maxp) << 16;
                        info2 |= (EHCI_TUNE_MULT_HS << 30);
                } else {                /* PIPE_INTERRUPT */
                        info1 |= max_packet (maxp) << 16;
                        info2 |= hb_mult (maxp) << 30;
                }
                break;
        default:
                dbg ("bogus dev %p speed %d", urb->dev, urb->dev->speed);
done:
                qh_put (qh);
                return NULL;
        }

        /* NOTE:  if (PIPE_INTERRUPT) { scheduler sets s-mask } */

        /* init as live, toggle clear, advance to dummy */
        qh->qh_state = QH_STATE_IDLE;
        hw = qh->hw;
        hw->hw_info1 = cpu_to_hc32(ehci, info1);
        hw->hw_info2 = cpu_to_hc32(ehci, info2);
        usb_settoggle (urb->dev, usb_pipeendpoint (urb->pipe), !is_input, 1);
        qh_refresh (ehci, qh);
        return qh;
}

/*-------------------------------------------------------------------------*/

/* move qh (and its qtds) onto async queue; maybe enable queue.  */

static void qh_link_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        __hc32          dma = QH_NEXT(ehci, qh->qh_dma);
        struct ehci_qh  *head;

        /* Don't link a QH if there's a Clear-TT-Buffer pending */
        if (unlikely(qh->clearing_tt))
                return;

        WARN_ON(qh->qh_state != QH_STATE_IDLE);

        /* (re)start the async schedule? */
        head = ehci->async;
        timer_action_done (ehci, TIMER_ASYNC_OFF);
        if (!head->qh_next.qh) {
                u32     cmd = ehci_readl(ehci, &ehci->regs->command);

                if (!(cmd & CMD_ASE)) {
                        /* in case a clear of CMD_ASE didn't take yet */
                        (void)handshake(ehci, &ehci->regs->status,
                                        STS_ASS, 0, 150);
                        cmd |= CMD_ASE | CMD_RUN;
                        ehci_writel(ehci, cmd, &ehci->regs->command);
                        ehci_to_hcd(ehci)->state = HC_STATE_RUNNING;
                        /* posted write need not be known to HC yet ... */
                }
        }

        /* clear halt and/or toggle; and maybe recover from silicon quirk */
        qh_refresh(ehci, qh);

        /* splice right after start */
        qh->qh_next = head->qh_next;
        qh->hw->hw_next = head->hw->hw_next;
        wmb ();

        head->qh_next.qh = qh;
        head->hw->hw_next = dma;

        qh_get(qh);
        qh->xacterrs = 0;
        qh->qh_state = QH_STATE_LINKED;
        /* qtd completions reported later by interrupt */
}

/*-------------------------------------------------------------------------*/

/*
 * For control/bulk/interrupt, return QH with these TDs appended.
 * Allocates and initializes the QH if necessary.
 * Returns null if it can't allocate a QH it needs to.
 * If the QH has TDs (urbs) already, that's great.
 */
static struct ehci_qh *qh_append_tds (
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        struct list_head        *qtd_list,
        int                     epnum,
        void                    **ptr

)
{
        struct ehci_qh          *qh = NULL;
        __hc32                  qh_addr_mask = cpu_to_hc32(ehci, 0x7f);

        qh = (struct ehci_qh *) *ptr;
        if (unlikely (qh == NULL)) {
                /* can't sleep here, we have ehci->lock... */
                qh = qh_make (ehci, urb, GFP_ATOMIC);
                *ptr = qh;
        }
        if (likely (qh != NULL)) {
                struct ehci_qtd *qtd;

                if (unlikely (list_empty (qtd_list)))
                        qtd = NULL;
                else
                        qtd = list_entry (qtd_list->next, struct ehci_qtd,
                                        qtd_list);

                /* control qh may need patching ... */
                if (unlikely (epnum == 0)) {

                        /* usb_reset_device() briefly reverts to address 0 */
                        if (usb_pipedevice (urb->pipe) == 0)
                                qh->hw->hw_info1 &= ~qh_addr_mask;
                }

                /* just one way to queue requests: swap with the dummy qtd.
                 * only hc or qh_refresh() ever modify the overlay.
                 */
                if (likely (qtd != NULL)) {
                        struct ehci_qtd         *dummy;
                        dma_addr_t              dma;
                        __hc32                  token;

                        /* to avoid racing the HC, use the dummy td instead of
                         * the first td of our list (becomes new dummy).  both
                         * tds stay deactivated until we're done, when the
                         * HC is allowed to fetch the old dummy (4.10.2).
                         */
                        token = qtd->hw_token;
                        qtd->hw_token = HALT_BIT(ehci);
                        wmb ();
                        dummy = qh->dummy;

                        dma = dummy->qtd_dma;
                        *dummy = *qtd;
                        dummy->qtd_dma = dma;

                        list_del (&qtd->qtd_list);
                        list_add (&dummy->qtd_list, qtd_list);
                        list_splice_tail(qtd_list, &qh->qtd_list);

                        ehci_qtd_init(ehci, qtd, qtd->qtd_dma);
                        qh->dummy = qtd;

                        /* hc must see the new dummy at list end */
                        dma = qtd->qtd_dma;
                        qtd = list_entry (qh->qtd_list.prev,
                                        struct ehci_qtd, qtd_list);
                        qtd->hw_next = QTD_NEXT(ehci, dma);

                        /* let the hc process these next qtds */
                        wmb ();
                        dummy->hw_token = token;

                        urb->hcpriv = qh_get (qh);
                }
        }
        return qh;
}

/*-------------------------------------------------------------------------*/

static int
submit_async (
        struct ehci_hcd         *ehci,
        struct urb              *urb,
        struct list_head        *qtd_list,
        gfp_t                   mem_flags
) {
        struct ehci_qtd         *qtd;
        int                     epnum;
        unsigned long           flags;
        struct ehci_qh          *qh = NULL;
        int                     rc;

        qtd = list_entry (qtd_list->next, struct ehci_qtd, qtd_list);
        epnum = urb->ep->desc.bEndpointAddress;

#ifdef EHCI_URB_TRACE
        ehci_dbg (ehci,
                "%s %s urb %p ep%d%s len %d, qtd %p [qh %p]\n",
                __func__, urb->dev->devpath, urb,
                epnum & 0x0f, (epnum & USB_DIR_IN) ? "in" : "out",
                urb->transfer_buffer_length,
                qtd, urb->ep->hcpriv);
#endif

        spin_lock_irqsave (&ehci->lock, flags);
        if (unlikely(!test_bit(HCD_FLAG_HW_ACCESSIBLE,
                               &ehci_to_hcd(ehci)->flags))) {
                rc = -ESHUTDOWN;
                goto done;
        }
        rc = usb_hcd_link_urb_to_ep(ehci_to_hcd(ehci), urb);
        if (unlikely(rc))
                goto done;

        qh = qh_append_tds(ehci, urb, qtd_list, epnum, &urb->ep->hcpriv);
        if (unlikely(qh == NULL)) {
                usb_hcd_unlink_urb_from_ep(ehci_to_hcd(ehci), urb);
                rc = -ENOMEM;
                goto done;
        }

        /* Control/bulk operations through TTs don't need scheduling,
         * the HC and TT handle it when the TT has a buffer ready.
         */
        if (likely (qh->qh_state == QH_STATE_IDLE))
                qh_link_async(ehci, qh);
 done:
        spin_unlock_irqrestore (&ehci->lock, flags);
        if (unlikely (qh == NULL))
                qtd_list_free (ehci, urb, qtd_list);
        return rc;
}

/*-------------------------------------------------------------------------*/

/* the async qh for the qtds being reclaimed are now unlinked from the HC */

static void end_unlink_async (struct ehci_hcd *ehci)
{
        struct ehci_qh          *qh = ehci->reclaim;
        struct ehci_qh          *next;

        iaa_watchdog_done(ehci);

        // qh->hw_next = cpu_to_hc32(qh->qh_dma);
        qh->qh_state = QH_STATE_IDLE;
        qh->qh_next.qh = NULL;
        qh_put (qh);                    // refcount from reclaim

        /* other unlink(s) may be pending (in QH_STATE_UNLINK_WAIT) */
        next = qh->reclaim;
        ehci->reclaim = next;
        qh->reclaim = NULL;

        qh_completions (ehci, qh);

        if (!list_empty (&qh->qtd_list)
                        && HC_IS_RUNNING (ehci_to_hcd(ehci)->state))
                qh_link_async (ehci, qh);
        else {
                /* it's not free to turn the async schedule on/off; leave it
                 * active but idle for a while once it empties.
                 */
                if (HC_IS_RUNNING (ehci_to_hcd(ehci)->state)
                                && ehci->async->qh_next.qh == NULL)
                        timer_action (ehci, TIMER_ASYNC_OFF);
        }
        qh_put(qh);                     /* refcount from async list */

        if (next) {
                ehci->reclaim = NULL;
                start_unlink_async (ehci, next);
        }
}

/* makes sure the async qh will become idle */
/* caller must own ehci->lock */

static void start_unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
        int             cmd = ehci_readl(ehci, &ehci->regs->command);
        struct ehci_qh  *prev;

#ifdef DEBUG
        assert_spin_locked(&ehci->lock);
        if (ehci->reclaim
                        || (qh->qh_state != QH_STATE_LINKED
                                && qh->qh_state != QH_STATE_UNLINK_WAIT)
                        )
                BUG ();
#endif

        /* stop async schedule right now? */
        if (unlikely (qh == ehci->async)) {
                /* can't get here without STS_ASS set */
                if (ehci_to_hcd(ehci)->state != HC_STATE_HALT
                                && !ehci->reclaim) {
                        /* ... and CMD_IAAD clear */
                        ehci_writel(ehci, cmd & ~CMD_ASE,
                                    &ehci->regs->command);
                        wmb ();
                        // handshake later, if we need to
                        timer_action_done (ehci, TIMER_ASYNC_OFF);
                }
                return;
        }

        qh->qh_state = QH_STATE_UNLINK;
        ehci->reclaim = qh = qh_get (qh);

        prev = ehci->async;
        while (prev->qh_next.qh != qh)
                prev = prev->qh_next.qh;

        prev->hw->hw_next = qh->hw->hw_next;
        prev->qh_next = qh->qh_next;
        wmb ();

        /* If the controller isn't running, we don't have to wait for it */
        if (unlikely(!HC_IS_RUNNING(ehci_to_hcd(ehci)->state))) {
                /* if (unlikely (qh->reclaim != 0))
                 *      this will recurse, probably not much
                 */
                end_unlink_async (ehci);
                return;
        }

        cmd |= CMD_IAAD;
        ehci_writel(ehci, cmd, &ehci->regs->command);
        (void)ehci_readl(ehci, &ehci->regs->command);
        iaa_watchdog_start(ehci);
}

/*-------------------------------------------------------------------------*/

static void scan_async (struct ehci_hcd *ehci)
{
        struct ehci_qh          *qh;
        enum ehci_timer_action  action = TIMER_IO_WATCHDOG;

        ehci->stamp = ehci_readl(ehci, &ehci->regs->frame_index);
        timer_action_done (ehci, TIMER_ASYNC_SHRINK);
rescan:
        qh = ehci->async->qh_next.qh;
        if (likely (qh != NULL)) {
                do {
                        /* clean any finished work for this qh */
                        if (!list_empty (&qh->qtd_list)
                                        && qh->stamp != ehci->stamp) {
                                int temp;

                                /* unlinks could happen here; completion
                                 * reporting drops the lock.  rescan using
                                 * the latest schedule, but don't rescan
                                 * qhs we already finished (no looping).
                                 */
                                qh = qh_get (qh);
                                qh->stamp = ehci->stamp;
                                temp = qh_completions (ehci, qh);
                                if (qh->needs_rescan)
                                        unlink_async(ehci, qh);
                                qh_put (qh);
                                if (temp != 0) {
                                        goto rescan;
                                }
                        }

                        /* unlink idle entries, reducing DMA usage as well
                         * as HCD schedule-scanning costs.  delay for any qh
                         * we just scanned, there's a not-unusual case that it
                         * doesn't stay idle for long.
                         * (plus, avoids some kind of re-activation race.)
                         */
                        if (list_empty(&qh->qtd_list)
                                        && qh->qh_state == QH_STATE_LINKED) {
                                if (!ehci->reclaim
                                        && ((ehci->stamp - qh->stamp) & 0x1fff)
                                                >= (EHCI_SHRINK_FRAMES * 8))
                                        start_unlink_async(ehci, qh);
                                else
                                        action = TIMER_ASYNC_SHRINK;
                        }

                        qh = qh->qh_next.qh;
                } while (qh);
        }
        if (action == TIMER_ASYNC_SHRINK)
                timer_action (ehci, TIMER_ASYNC_SHRINK);
}