linux/drivers/tty/ehv_bytechan.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/* ePAPR hypervisor byte channel device driver
   3 *
   4 * Copyright 2009-2011 Freescale Semiconductor, Inc.
   5 *
   6 * Author: Timur Tabi <timur@freescale.com>
   7 *
   8 * This driver support three distinct interfaces, all of which are related to
   9 * ePAPR hypervisor byte channels.
  10 *
  11 * 1) An early-console (udbg) driver.  This provides early console output
  12 * through a byte channel.  The byte channel handle must be specified in a
  13 * Kconfig option.
  14 *
  15 * 2) A normal console driver.  Output is sent to the byte channel designated
  16 * for stdout in the device tree.  The console driver is for handling kernel
  17 * printk calls.
  18 *
  19 * 3) A tty driver, which is used to handle user-space input and output.  The
  20 * byte channel used for the console is designated as the default tty.
  21 */
  22
  23#include <linux/init.h>
  24#include <linux/slab.h>
  25#include <linux/err.h>
  26#include <linux/interrupt.h>
  27#include <linux/fs.h>
  28#include <linux/poll.h>
  29#include <asm/epapr_hcalls.h>
  30#include <linux/of.h>
  31#include <linux/of_irq.h>
  32#include <linux/platform_device.h>
  33#include <linux/cdev.h>
  34#include <linux/console.h>
  35#include <linux/tty.h>
  36#include <linux/tty_flip.h>
  37#include <linux/circ_buf.h>
  38#include <asm/udbg.h>
  39
  40/* The size of the transmit circular buffer.  This must be a power of two. */
  41#define BUF_SIZE        2048
  42
  43/* Per-byte channel private data */
  44struct ehv_bc_data {
  45        struct device *dev;
  46        struct tty_port port;
  47        uint32_t handle;
  48        unsigned int rx_irq;
  49        unsigned int tx_irq;
  50
  51        spinlock_t lock;        /* lock for transmit buffer */
  52        unsigned char buf[BUF_SIZE];    /* transmit circular buffer */
  53        unsigned int head;      /* circular buffer head */
  54        unsigned int tail;      /* circular buffer tail */
  55
  56        int tx_irq_enabled;     /* true == TX interrupt is enabled */
  57};
  58
  59/* Array of byte channel objects */
  60static struct ehv_bc_data *bcs;
  61
  62/* Byte channel handle for stdout (and stdin), taken from device tree */
  63static unsigned int stdout_bc;
  64
  65/* Virtual IRQ for the byte channel handle for stdin, taken from device tree */
  66static unsigned int stdout_irq;
  67
  68/**************************** SUPPORT FUNCTIONS ****************************/
  69
  70/*
  71 * Enable the transmit interrupt
  72 *
  73 * Unlike a serial device, byte channels have no mechanism for disabling their
  74 * own receive or transmit interrupts.  To emulate that feature, we toggle
  75 * the IRQ in the kernel.
  76 *
  77 * We cannot just blindly call enable_irq() or disable_irq(), because these
  78 * calls are reference counted.  This means that we cannot call enable_irq()
  79 * if interrupts are already enabled.  This can happen in two situations:
  80 *
  81 * 1. The tty layer makes two back-to-back calls to ehv_bc_tty_write()
  82 * 2. A transmit interrupt occurs while executing ehv_bc_tx_dequeue()
  83 *
  84 * To work around this, we keep a flag to tell us if the IRQ is enabled or not.
  85 */
  86static void enable_tx_interrupt(struct ehv_bc_data *bc)
  87{
  88        if (!bc->tx_irq_enabled) {
  89                enable_irq(bc->tx_irq);
  90                bc->tx_irq_enabled = 1;
  91        }
  92}
  93
  94static void disable_tx_interrupt(struct ehv_bc_data *bc)
  95{
  96        if (bc->tx_irq_enabled) {
  97                disable_irq_nosync(bc->tx_irq);
  98                bc->tx_irq_enabled = 0;
  99        }
 100}
 101
 102/*
 103 * find the byte channel handle to use for the console
 104 *
 105 * The byte channel to be used for the console is specified via a "stdout"
 106 * property in the /chosen node.
 107 */
 108static int find_console_handle(void)
 109{
 110        struct device_node *np = of_stdout;
 111        const uint32_t *iprop;
 112
 113        /* We don't care what the aliased node is actually called.  We only
 114         * care if it's compatible with "epapr,hv-byte-channel", because that
 115         * indicates that it's a byte channel node.
 116         */
 117        if (!np || !of_device_is_compatible(np, "epapr,hv-byte-channel"))
 118                return 0;
 119
 120        stdout_irq = irq_of_parse_and_map(np, 0);
 121        if (stdout_irq == NO_IRQ) {
 122                pr_err("ehv-bc: no 'interrupts' property in %pOF node\n", np);
 123                return 0;
 124        }
 125
 126        /*
 127         * The 'hv-handle' property contains the handle for this byte channel.
 128         */
 129        iprop = of_get_property(np, "hv-handle", NULL);
 130        if (!iprop) {
 131                pr_err("ehv-bc: no 'hv-handle' property in %pOFn node\n",
 132                       np);
 133                return 0;
 134        }
 135        stdout_bc = be32_to_cpu(*iprop);
 136        return 1;
 137}
 138
 139static unsigned int local_ev_byte_channel_send(unsigned int handle,
 140                                               unsigned int *count,
 141                                               const char *p)
 142{
 143        char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
 144        unsigned int c = *count;
 145
 146        if (c < sizeof(buffer)) {
 147                memcpy(buffer, p, c);
 148                memset(&buffer[c], 0, sizeof(buffer) - c);
 149                p = buffer;
 150        }
 151        return ev_byte_channel_send(handle, count, p);
 152}
 153
 154/*************************** EARLY CONSOLE DRIVER ***************************/
 155
 156#ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
 157
 158/*
 159 * send a byte to a byte channel, wait if necessary
 160 *
 161 * This function sends a byte to a byte channel, and it waits and
 162 * retries if the byte channel is full.  It returns if the character
 163 * has been sent, or if some error has occurred.
 164 *
 165 */
 166static void byte_channel_spin_send(const char data)
 167{
 168        int ret, count;
 169
 170        do {
 171                count = 1;
 172                ret = local_ev_byte_channel_send(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
 173                                           &count, &data);
 174        } while (ret == EV_EAGAIN);
 175}
 176
 177/*
 178 * The udbg subsystem calls this function to display a single character.
 179 * We convert CR to a CR/LF.
 180 */
 181static void ehv_bc_udbg_putc(char c)
 182{
 183        if (c == '\n')
 184                byte_channel_spin_send('\r');
 185
 186        byte_channel_spin_send(c);
 187}
 188
 189/*
 190 * early console initialization
 191 *
 192 * PowerPC kernels support an early printk console, also known as udbg.
 193 * This function must be called via the ppc_md.init_early function pointer.
 194 * At this point, the device tree has been unflattened, so we can obtain the
 195 * byte channel handle for stdout.
 196 *
 197 * We only support displaying of characters (putc).  We do not support
 198 * keyboard input.
 199 */
 200void __init udbg_init_ehv_bc(void)
 201{
 202        unsigned int rx_count, tx_count;
 203        unsigned int ret;
 204
 205        /* Verify the byte channel handle */
 206        ret = ev_byte_channel_poll(CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE,
 207                                   &rx_count, &tx_count);
 208        if (ret)
 209                return;
 210
 211        udbg_putc = ehv_bc_udbg_putc;
 212        register_early_udbg_console();
 213
 214        udbg_printf("ehv-bc: early console using byte channel handle %u\n",
 215                    CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
 216}
 217
 218#endif
 219
 220/****************************** CONSOLE DRIVER ******************************/
 221
 222static struct tty_driver *ehv_bc_driver;
 223
 224/*
 225 * Byte channel console sending worker function.
 226 *
 227 * For consoles, if the output buffer is full, we should just spin until it
 228 * clears.
 229 */
 230static int ehv_bc_console_byte_channel_send(unsigned int handle, const char *s,
 231                             unsigned int count)
 232{
 233        unsigned int len;
 234        int ret = 0;
 235
 236        while (count) {
 237                len = min_t(unsigned int, count, EV_BYTE_CHANNEL_MAX_BYTES);
 238                do {
 239                        ret = local_ev_byte_channel_send(handle, &len, s);
 240                } while (ret == EV_EAGAIN);
 241                count -= len;
 242                s += len;
 243        }
 244
 245        return ret;
 246}
 247
 248/*
 249 * write a string to the console
 250 *
 251 * This function gets called to write a string from the kernel, typically from
 252 * a printk().  This function spins until all data is written.
 253 *
 254 * We copy the data to a temporary buffer because we need to insert a \r in
 255 * front of every \n.  It's more efficient to copy the data to the buffer than
 256 * it is to make multiple hcalls for each character or each newline.
 257 */
 258static void ehv_bc_console_write(struct console *co, const char *s,
 259                                 unsigned int count)
 260{
 261        char s2[EV_BYTE_CHANNEL_MAX_BYTES];
 262        unsigned int i, j = 0;
 263        char c;
 264
 265        for (i = 0; i < count; i++) {
 266                c = *s++;
 267
 268                if (c == '\n')
 269                        s2[j++] = '\r';
 270
 271                s2[j++] = c;
 272                if (j >= (EV_BYTE_CHANNEL_MAX_BYTES - 1)) {
 273                        if (ehv_bc_console_byte_channel_send(stdout_bc, s2, j))
 274                                return;
 275                        j = 0;
 276                }
 277        }
 278
 279        if (j)
 280                ehv_bc_console_byte_channel_send(stdout_bc, s2, j);
 281}
 282
 283/*
 284 * When /dev/console is opened, the kernel iterates the console list looking
 285 * for one with ->device and then calls that method. On success, it expects
 286 * the passed-in int* to contain the minor number to use.
 287 */
 288static struct tty_driver *ehv_bc_console_device(struct console *co, int *index)
 289{
 290        *index = co->index;
 291
 292        return ehv_bc_driver;
 293}
 294
 295static struct console ehv_bc_console = {
 296        .name           = "ttyEHV",
 297        .write          = ehv_bc_console_write,
 298        .device         = ehv_bc_console_device,
 299        .flags          = CON_PRINTBUFFER | CON_ENABLED,
 300};
 301
 302/*
 303 * Console initialization
 304 *
 305 * This is the first function that is called after the device tree is
 306 * available, so here is where we determine the byte channel handle and IRQ for
 307 * stdout/stdin, even though that information is used by the tty and character
 308 * drivers.
 309 */
 310static int __init ehv_bc_console_init(void)
 311{
 312        if (!find_console_handle()) {
 313                pr_debug("ehv-bc: stdout is not a byte channel\n");
 314                return -ENODEV;
 315        }
 316
 317#ifdef CONFIG_PPC_EARLY_DEBUG_EHV_BC
 318        /* Print a friendly warning if the user chose the wrong byte channel
 319         * handle for udbg.
 320         */
 321        if (stdout_bc != CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE)
 322                pr_warn("ehv-bc: udbg handle %u is not the stdout handle\n",
 323                        CONFIG_PPC_EARLY_DEBUG_EHV_BC_HANDLE);
 324#endif
 325
 326        /* add_preferred_console() must be called before register_console(),
 327           otherwise it won't work.  However, we don't want to enumerate all the
 328           byte channels here, either, since we only care about one. */
 329
 330        add_preferred_console(ehv_bc_console.name, ehv_bc_console.index, NULL);
 331        register_console(&ehv_bc_console);
 332
 333        pr_info("ehv-bc: registered console driver for byte channel %u\n",
 334                stdout_bc);
 335
 336        return 0;
 337}
 338console_initcall(ehv_bc_console_init);
 339
 340/******************************** TTY DRIVER ********************************/
 341
 342/*
 343 * byte channel receive interrupt handler
 344 *
 345 * This ISR is called whenever data is available on a byte channel.
 346 */
 347static irqreturn_t ehv_bc_tty_rx_isr(int irq, void *data)
 348{
 349        struct ehv_bc_data *bc = data;
 350        unsigned int rx_count, tx_count, len;
 351        int count;
 352        char buffer[EV_BYTE_CHANNEL_MAX_BYTES];
 353        int ret;
 354
 355        /* Find out how much data needs to be read, and then ask the TTY layer
 356         * if it can handle that much.  We want to ensure that every byte we
 357         * read from the byte channel will be accepted by the TTY layer.
 358         */
 359        ev_byte_channel_poll(bc->handle, &rx_count, &tx_count);
 360        count = tty_buffer_request_room(&bc->port, rx_count);
 361
 362        /* 'count' is the maximum amount of data the TTY layer can accept at
 363         * this time.  However, during testing, I was never able to get 'count'
 364         * to be less than 'rx_count'.  I'm not sure whether I'm calling it
 365         * correctly.
 366         */
 367
 368        while (count > 0) {
 369                len = min_t(unsigned int, count, sizeof(buffer));
 370
 371                /* Read some data from the byte channel.  This function will
 372                 * never return more than EV_BYTE_CHANNEL_MAX_BYTES bytes.
 373                 */
 374                ev_byte_channel_receive(bc->handle, &len, buffer);
 375
 376                /* 'len' is now the amount of data that's been received. 'len'
 377                 * can't be zero, and most likely it's equal to one.
 378                 */
 379
 380                /* Pass the received data to the tty layer. */
 381                ret = tty_insert_flip_string(&bc->port, buffer, len);
 382
 383                /* 'ret' is the number of bytes that the TTY layer accepted.
 384                 * If it's not equal to 'len', then it means the buffer is
 385                 * full, which should never happen.  If it does happen, we can
 386                 * exit gracefully, but we drop the last 'len - ret' characters
 387                 * that we read from the byte channel.
 388                 */
 389                if (ret != len)
 390                        break;
 391
 392                count -= len;
 393        }
 394
 395        /* Tell the tty layer that we're done. */
 396        tty_flip_buffer_push(&bc->port);
 397
 398        return IRQ_HANDLED;
 399}
 400
 401/*
 402 * dequeue the transmit buffer to the hypervisor
 403 *
 404 * This function, which can be called in interrupt context, dequeues as much
 405 * data as possible from the transmit buffer to the byte channel.
 406 */
 407static void ehv_bc_tx_dequeue(struct ehv_bc_data *bc)
 408{
 409        unsigned int count;
 410        unsigned int len, ret;
 411        unsigned long flags;
 412
 413        do {
 414                spin_lock_irqsave(&bc->lock, flags);
 415                len = min_t(unsigned int,
 416                            CIRC_CNT_TO_END(bc->head, bc->tail, BUF_SIZE),
 417                            EV_BYTE_CHANNEL_MAX_BYTES);
 418
 419                ret = local_ev_byte_channel_send(bc->handle, &len, bc->buf + bc->tail);
 420
 421                /* 'len' is valid only if the return code is 0 or EV_EAGAIN */
 422                if (!ret || (ret == EV_EAGAIN))
 423                        bc->tail = (bc->tail + len) & (BUF_SIZE - 1);
 424
 425                count = CIRC_CNT(bc->head, bc->tail, BUF_SIZE);
 426                spin_unlock_irqrestore(&bc->lock, flags);
 427        } while (count && !ret);
 428
 429        spin_lock_irqsave(&bc->lock, flags);
 430        if (CIRC_CNT(bc->head, bc->tail, BUF_SIZE))
 431                /*
 432                 * If we haven't emptied the buffer, then enable the TX IRQ.
 433                 * We'll get an interrupt when there's more room in the
 434                 * hypervisor's output buffer.
 435                 */
 436                enable_tx_interrupt(bc);
 437        else
 438                disable_tx_interrupt(bc);
 439        spin_unlock_irqrestore(&bc->lock, flags);
 440}
 441
 442/*
 443 * byte channel transmit interrupt handler
 444 *
 445 * This ISR is called whenever space becomes available for transmitting
 446 * characters on a byte channel.
 447 */
 448static irqreturn_t ehv_bc_tty_tx_isr(int irq, void *data)
 449{
 450        struct ehv_bc_data *bc = data;
 451
 452        ehv_bc_tx_dequeue(bc);
 453        tty_port_tty_wakeup(&bc->port);
 454
 455        return IRQ_HANDLED;
 456}
 457
 458/*
 459 * This function is called when the tty layer has data for us send.  We store
 460 * the data first in a circular buffer, and then dequeue as much of that data
 461 * as possible.
 462 *
 463 * We don't need to worry about whether there is enough room in the buffer for
 464 * all the data.  The purpose of ehv_bc_tty_write_room() is to tell the tty
 465 * layer how much data it can safely send to us.  We guarantee that
 466 * ehv_bc_tty_write_room() will never lie, so the tty layer will never send us
 467 * too much data.
 468 */
 469static int ehv_bc_tty_write(struct tty_struct *ttys, const unsigned char *s,
 470                            int count)
 471{
 472        struct ehv_bc_data *bc = ttys->driver_data;
 473        unsigned long flags;
 474        unsigned int len;
 475        unsigned int written = 0;
 476
 477        while (1) {
 478                spin_lock_irqsave(&bc->lock, flags);
 479                len = CIRC_SPACE_TO_END(bc->head, bc->tail, BUF_SIZE);
 480                if (count < len)
 481                        len = count;
 482                if (len) {
 483                        memcpy(bc->buf + bc->head, s, len);
 484                        bc->head = (bc->head + len) & (BUF_SIZE - 1);
 485                }
 486                spin_unlock_irqrestore(&bc->lock, flags);
 487                if (!len)
 488                        break;
 489
 490                s += len;
 491                count -= len;
 492                written += len;
 493        }
 494
 495        ehv_bc_tx_dequeue(bc);
 496
 497        return written;
 498}
 499
 500/*
 501 * This function can be called multiple times for a given tty_struct, which is
 502 * why we initialize bc->ttys in ehv_bc_tty_port_activate() instead.
 503 *
 504 * The tty layer will still call this function even if the device was not
 505 * registered (i.e. tty_register_device() was not called).  This happens
 506 * because tty_register_device() is optional and some legacy drivers don't
 507 * use it.  So we need to check for that.
 508 */
 509static int ehv_bc_tty_open(struct tty_struct *ttys, struct file *filp)
 510{
 511        struct ehv_bc_data *bc = &bcs[ttys->index];
 512
 513        if (!bc->dev)
 514                return -ENODEV;
 515
 516        return tty_port_open(&bc->port, ttys, filp);
 517}
 518
 519/*
 520 * Amazingly, if ehv_bc_tty_open() returns an error code, the tty layer will
 521 * still call this function to close the tty device.  So we can't assume that
 522 * the tty port has been initialized.
 523 */
 524static void ehv_bc_tty_close(struct tty_struct *ttys, struct file *filp)
 525{
 526        struct ehv_bc_data *bc = &bcs[ttys->index];
 527
 528        if (bc->dev)
 529                tty_port_close(&bc->port, ttys, filp);
 530}
 531
 532/*
 533 * Return the amount of space in the output buffer
 534 *
 535 * This is actually a contract between the driver and the tty layer outlining
 536 * how much write room the driver can guarantee will be sent OR BUFFERED.  This
 537 * driver MUST honor the return value.
 538 */
 539static unsigned int ehv_bc_tty_write_room(struct tty_struct *ttys)
 540{
 541        struct ehv_bc_data *bc = ttys->driver_data;
 542        unsigned long flags;
 543        unsigned int count;
 544
 545        spin_lock_irqsave(&bc->lock, flags);
 546        count = CIRC_SPACE(bc->head, bc->tail, BUF_SIZE);
 547        spin_unlock_irqrestore(&bc->lock, flags);
 548
 549        return count;
 550}
 551
 552/*
 553 * Stop sending data to the tty layer
 554 *
 555 * This function is called when the tty layer's input buffers are getting full,
 556 * so the driver should stop sending it data.  The easiest way to do this is to
 557 * disable the RX IRQ, which will prevent ehv_bc_tty_rx_isr() from being
 558 * called.
 559 *
 560 * The hypervisor will continue to queue up any incoming data.  If there is any
 561 * data in the queue when the RX interrupt is enabled, we'll immediately get an
 562 * RX interrupt.
 563 */
 564static void ehv_bc_tty_throttle(struct tty_struct *ttys)
 565{
 566        struct ehv_bc_data *bc = ttys->driver_data;
 567
 568        disable_irq(bc->rx_irq);
 569}
 570
 571/*
 572 * Resume sending data to the tty layer
 573 *
 574 * This function is called after previously calling ehv_bc_tty_throttle().  The
 575 * tty layer's input buffers now have more room, so the driver can resume
 576 * sending it data.
 577 */
 578static void ehv_bc_tty_unthrottle(struct tty_struct *ttys)
 579{
 580        struct ehv_bc_data *bc = ttys->driver_data;
 581
 582        /* If there is any data in the queue when the RX interrupt is enabled,
 583         * we'll immediately get an RX interrupt.
 584         */
 585        enable_irq(bc->rx_irq);
 586}
 587
 588static void ehv_bc_tty_hangup(struct tty_struct *ttys)
 589{
 590        struct ehv_bc_data *bc = ttys->driver_data;
 591
 592        ehv_bc_tx_dequeue(bc);
 593        tty_port_hangup(&bc->port);
 594}
 595
 596/*
 597 * TTY driver operations
 598 *
 599 * If we could ask the hypervisor how much data is still in the TX buffer, or
 600 * at least how big the TX buffers are, then we could implement the
 601 * .wait_until_sent and .chars_in_buffer functions.
 602 */
 603static const struct tty_operations ehv_bc_ops = {
 604        .open           = ehv_bc_tty_open,
 605        .close          = ehv_bc_tty_close,
 606        .write          = ehv_bc_tty_write,
 607        .write_room     = ehv_bc_tty_write_room,
 608        .throttle       = ehv_bc_tty_throttle,
 609        .unthrottle     = ehv_bc_tty_unthrottle,
 610        .hangup         = ehv_bc_tty_hangup,
 611};
 612
 613/*
 614 * initialize the TTY port
 615 *
 616 * This function will only be called once, no matter how many times
 617 * ehv_bc_tty_open() is called.  That's why we register the ISR here, and also
 618 * why we initialize tty_struct-related variables here.
 619 */
 620static int ehv_bc_tty_port_activate(struct tty_port *port,
 621                                    struct tty_struct *ttys)
 622{
 623        struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
 624        int ret;
 625
 626        ttys->driver_data = bc;
 627
 628        ret = request_irq(bc->rx_irq, ehv_bc_tty_rx_isr, 0, "ehv-bc", bc);
 629        if (ret < 0) {
 630                dev_err(bc->dev, "could not request rx irq %u (ret=%i)\n",
 631                       bc->rx_irq, ret);
 632                return ret;
 633        }
 634
 635        /* request_irq also enables the IRQ */
 636        bc->tx_irq_enabled = 1;
 637
 638        ret = request_irq(bc->tx_irq, ehv_bc_tty_tx_isr, 0, "ehv-bc", bc);
 639        if (ret < 0) {
 640                dev_err(bc->dev, "could not request tx irq %u (ret=%i)\n",
 641                       bc->tx_irq, ret);
 642                free_irq(bc->rx_irq, bc);
 643                return ret;
 644        }
 645
 646        /* The TX IRQ is enabled only when we can't write all the data to the
 647         * byte channel at once, so by default it's disabled.
 648         */
 649        disable_tx_interrupt(bc);
 650
 651        return 0;
 652}
 653
 654static void ehv_bc_tty_port_shutdown(struct tty_port *port)
 655{
 656        struct ehv_bc_data *bc = container_of(port, struct ehv_bc_data, port);
 657
 658        free_irq(bc->tx_irq, bc);
 659        free_irq(bc->rx_irq, bc);
 660}
 661
 662static const struct tty_port_operations ehv_bc_tty_port_ops = {
 663        .activate = ehv_bc_tty_port_activate,
 664        .shutdown = ehv_bc_tty_port_shutdown,
 665};
 666
 667static int ehv_bc_tty_probe(struct platform_device *pdev)
 668{
 669        struct device_node *np = pdev->dev.of_node;
 670        struct ehv_bc_data *bc;
 671        const uint32_t *iprop;
 672        unsigned int handle;
 673        int ret;
 674        static unsigned int index = 1;
 675        unsigned int i;
 676
 677        iprop = of_get_property(np, "hv-handle", NULL);
 678        if (!iprop) {
 679                dev_err(&pdev->dev, "no 'hv-handle' property in %pOFn node\n",
 680                        np);
 681                return -ENODEV;
 682        }
 683
 684        /* We already told the console layer that the index for the console
 685         * device is zero, so we need to make sure that we use that index when
 686         * we probe the console byte channel node.
 687         */
 688        handle = be32_to_cpu(*iprop);
 689        i = (handle == stdout_bc) ? 0 : index++;
 690        bc = &bcs[i];
 691
 692        bc->handle = handle;
 693        bc->head = 0;
 694        bc->tail = 0;
 695        spin_lock_init(&bc->lock);
 696
 697        bc->rx_irq = irq_of_parse_and_map(np, 0);
 698        bc->tx_irq = irq_of_parse_and_map(np, 1);
 699        if ((bc->rx_irq == NO_IRQ) || (bc->tx_irq == NO_IRQ)) {
 700                dev_err(&pdev->dev, "no 'interrupts' property in %pOFn node\n",
 701                        np);
 702                ret = -ENODEV;
 703                goto error;
 704        }
 705
 706        tty_port_init(&bc->port);
 707        bc->port.ops = &ehv_bc_tty_port_ops;
 708
 709        bc->dev = tty_port_register_device(&bc->port, ehv_bc_driver, i,
 710                        &pdev->dev);
 711        if (IS_ERR(bc->dev)) {
 712                ret = PTR_ERR(bc->dev);
 713                dev_err(&pdev->dev, "could not register tty (ret=%i)\n", ret);
 714                goto error;
 715        }
 716
 717        dev_set_drvdata(&pdev->dev, bc);
 718
 719        dev_info(&pdev->dev, "registered /dev/%s%u for byte channel %u\n",
 720                ehv_bc_driver->name, i, bc->handle);
 721
 722        return 0;
 723
 724error:
 725        tty_port_destroy(&bc->port);
 726        irq_dispose_mapping(bc->tx_irq);
 727        irq_dispose_mapping(bc->rx_irq);
 728
 729        memset(bc, 0, sizeof(struct ehv_bc_data));
 730        return ret;
 731}
 732
 733static const struct of_device_id ehv_bc_tty_of_ids[] = {
 734        { .compatible = "epapr,hv-byte-channel" },
 735        {}
 736};
 737
 738static struct platform_driver ehv_bc_tty_driver = {
 739        .driver = {
 740                .name = "ehv-bc",
 741                .of_match_table = ehv_bc_tty_of_ids,
 742                .suppress_bind_attrs = true,
 743        },
 744        .probe          = ehv_bc_tty_probe,
 745};
 746
 747/**
 748 * ehv_bc_init - ePAPR hypervisor byte channel driver initialization
 749 *
 750 * This function is called when this driver is loaded.
 751 */
 752static int __init ehv_bc_init(void)
 753{
 754        struct device_node *np;
 755        unsigned int count = 0; /* Number of elements in bcs[] */
 756        int ret;
 757
 758        pr_info("ePAPR hypervisor byte channel driver\n");
 759
 760        /* Count the number of byte channels */
 761        for_each_compatible_node(np, NULL, "epapr,hv-byte-channel")
 762                count++;
 763
 764        if (!count)
 765                return -ENODEV;
 766
 767        /* The array index of an element in bcs[] is the same as the tty index
 768         * for that element.  If you know the address of an element in the
 769         * array, then you can use pointer math (e.g. "bc - bcs") to get its
 770         * tty index.
 771         */
 772        bcs = kcalloc(count, sizeof(struct ehv_bc_data), GFP_KERNEL);
 773        if (!bcs)
 774                return -ENOMEM;
 775
 776        ehv_bc_driver = alloc_tty_driver(count);
 777        if (!ehv_bc_driver) {
 778                ret = -ENOMEM;
 779                goto err_free_bcs;
 780        }
 781
 782        ehv_bc_driver->driver_name = "ehv-bc";
 783        ehv_bc_driver->name = ehv_bc_console.name;
 784        ehv_bc_driver->type = TTY_DRIVER_TYPE_CONSOLE;
 785        ehv_bc_driver->subtype = SYSTEM_TYPE_CONSOLE;
 786        ehv_bc_driver->init_termios = tty_std_termios;
 787        ehv_bc_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
 788        tty_set_operations(ehv_bc_driver, &ehv_bc_ops);
 789
 790        ret = tty_register_driver(ehv_bc_driver);
 791        if (ret) {
 792                pr_err("ehv-bc: could not register tty driver (ret=%i)\n", ret);
 793                goto err_put_tty_driver;
 794        }
 795
 796        ret = platform_driver_register(&ehv_bc_tty_driver);
 797        if (ret) {
 798                pr_err("ehv-bc: could not register platform driver (ret=%i)\n",
 799                       ret);
 800                goto err_deregister_tty_driver;
 801        }
 802
 803        return 0;
 804
 805err_deregister_tty_driver:
 806        tty_unregister_driver(ehv_bc_driver);
 807err_put_tty_driver:
 808        put_tty_driver(ehv_bc_driver);
 809err_free_bcs:
 810        kfree(bcs);
 811
 812        return ret;
 813}
 814device_initcall(ehv_bc_init);
 815