// SPDX-License-Identifier: GPL-2.0
/*
 * Xpram.c -- the S/390 expanded memory RAM-disk
 *           
 * significant parts of this code are based on
 * the sbull device driver presented in
 * A. Rubini: Linux Device Drivers
 *
 * Author of XPRAM specific coding: Reinhard Buendgen
 *                                  buendgen@de.ibm.com
 * Rewrite for 2.5: Martin Schwidefsky <schwidefsky@de.ibm.com>
 *
 * External interfaces:
 *   Interfaces to linux kernel
 *        xpram_setup: read kernel parameters
 *   Device specific file operations
 *        xpram_iotcl
 *        xpram_open
 *
 * "ad-hoc" partitioning:
 *    the expanded memory can be partitioned among several devices 
 *    (with different minors). The partitioning set up can be
 *    set by kernel or module parameters (int devs & int sizes[])
 *
 * Potential future improvements:
 *   generic hard disk support to replace ad-hoc partitioning
 */

#define KMSG_COMPONENT "xpram"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/ctype.h>  /* isdigit, isxdigit */
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/blkdev.h>
#include <linux/blkpg.h>
#include <linux/hdreg.h>  /* HDIO_GETGEO */
#include <linux/device.h>
#include <linux/bio.h>
#include <linux/gfp.h>
#include <linux/uaccess.h>

#define XPRAM_NAME      "xpram"
#define XPRAM_DEVS      1       /* one partition */
#define XPRAM_MAX_DEVS  32      /* maximal number of devices (partitions) */

typedef struct {
        unsigned int    size;           /* size of xpram segment in pages */
        unsigned int    offset;         /* start page of xpram segment */
} xpram_device_t;

static xpram_device_t xpram_devices[XPRAM_MAX_DEVS];
static unsigned int xpram_sizes[XPRAM_MAX_DEVS];
static struct gendisk *xpram_disks[XPRAM_MAX_DEVS];
static unsigned int xpram_pages;
static int xpram_devs;

/*
 * Parameter parsing functions.
 */
static int devs = XPRAM_DEVS;
static char *sizes[XPRAM_MAX_DEVS];

module_param(devs, int, 0);
module_param_array(sizes, charp, NULL, 0);

MODULE_PARM_DESC(devs, "number of devices (\"partitions\"), " \
                 "the default is " __MODULE_STRING(XPRAM_DEVS) "\n");
MODULE_PARM_DESC(sizes, "list of device (partition) sizes " \
                 "the defaults are 0s \n" \
                 "All devices with size 0 equally partition the "
                 "remaining space on the expanded strorage not "
                 "claimed by explicit sizes\n");
MODULE_LICENSE("GPL");

/*
 * Copy expanded memory page (4kB) into main memory                  
 * Arguments                                                         
 *           page_addr:    address of target page                    
 *           xpage_index:  index of expandeded memory page           
 * Return value                                                      
 *           0:            if operation succeeds
 *           -EIO:         if pgin failed
 *           -ENXIO:       if xpram has vanished
 */
static int xpram_page_in (unsigned long page_addr, unsigned int xpage_index)
{
        int cc = 2;     /* return unused cc 2 if pgin traps */

        asm volatile(
                "       .insn   rre,0xb22e0000,%1,%2\n"  /* pgin %1,%2 */
                "0:     ipm     %0\n"
                "       srl     %0,28\n"
                "1:\n"
                EX_TABLE(0b,1b)
                : "+d" (cc) : "a" (__pa(page_addr)), "d" (xpage_index) : "cc");
        if (cc == 3)
                return -ENXIO;
        if (cc == 2)
                return -ENXIO;
        if (cc == 1)
                return -EIO;
        return 0;
}

/*
 * Copy a 4kB page of main memory to an expanded memory page          
 * Arguments                                                          
 *           page_addr:    address of source page                     
 *           xpage_index:  index of expandeded memory page            
 * Return value                                                       
 *           0:            if operation succeeds
 *           -EIO:         if pgout failed
 *           -ENXIO:       if xpram has vanished
 */
static long xpram_page_out (unsigned long page_addr, unsigned int xpage_index)
{
        int cc = 2;     /* return unused cc 2 if pgin traps */

        asm volatile(
                "       .insn   rre,0xb22f0000,%1,%2\n"  /* pgout %1,%2 */
                "0:     ipm     %0\n"
                "       srl     %0,28\n"
                "1:\n"
                EX_TABLE(0b,1b)
                : "+d" (cc) : "a" (__pa(page_addr)), "d" (xpage_index) : "cc");
        if (cc == 3)
                return -ENXIO;
        if (cc == 2)
                return -ENXIO;
        if (cc == 1)
                return -EIO;
        return 0;
}

/*
 * Check if xpram is available.
 */
static int __init xpram_present(void)
{
        unsigned long mem_page;
        int rc;

        mem_page = (unsigned long) __get_free_page(GFP_KERNEL);
        if (!mem_page)
                return -ENOMEM;
        rc = xpram_page_in(mem_page, 0);
        free_page(mem_page);
        return rc ? -ENXIO : 0;
}

/*
 * Return index of the last available xpram page.
 */
static unsigned long __init xpram_highest_page_index(void)
{
        unsigned int page_index, add_bit;
        unsigned long mem_page;

        mem_page = (unsigned long) __get_free_page(GFP_KERNEL);
        if (!mem_page)
                return 0;

        page_index = 0;
        add_bit = 1ULL << (sizeof(unsigned int)*8 - 1);
        while (add_bit > 0) {
                if (xpram_page_in(mem_page, page_index | add_bit) == 0)
                        page_index |= add_bit;
                add_bit >>= 1;
        }

        free_page (mem_page);

        return page_index;
}

/*
 * Block device make request function.
 */
static blk_qc_t xpram_submit_bio(struct bio *bio)
{
        xpram_device_t *xdev = bio->bi_bdev->bd_disk->private_data;
        struct bio_vec bvec;
        struct bvec_iter iter;
        unsigned int index;
        unsigned long page_addr;
        unsigned long bytes;

        blk_queue_split(&bio);

        if ((bio->bi_iter.bi_sector & 7) != 0 ||
            (bio->bi_iter.bi_size & 4095) != 0)
                /* Request is not page-aligned. */
                goto fail;
        if ((bio->bi_iter.bi_size >> 12) > xdev->size)
                /* Request size is no page-aligned. */
                goto fail;
        if ((bio->bi_iter.bi_sector >> 3) > 0xffffffffU - xdev->offset)
                goto fail;
        index = (bio->bi_iter.bi_sector >> 3) + xdev->offset;
        bio_for_each_segment(bvec, bio, iter) {
                page_addr = (unsigned long)
                        kmap(bvec.bv_page) + bvec.bv_offset;
                bytes = bvec.bv_len;
                if ((page_addr & 4095) != 0 || (bytes & 4095) != 0)
                        /* More paranoia. */
                        goto fail;
                while (bytes > 0) {
                        if (bio_data_dir(bio) == READ) {
                                if (xpram_page_in(page_addr, index) != 0)
                                        goto fail;
                        } else {
                                if (xpram_page_out(page_addr, index) != 0)
                                        goto fail;
                        }
                        page_addr += 4096;
                        bytes -= 4096;
                        index++;
                }
        }
        bio_endio(bio);
        return BLK_QC_T_NONE;
fail:
        bio_io_error(bio);
        return BLK_QC_T_NONE;
}

static int xpram_getgeo(struct block_device *bdev, struct hd_geometry *geo)
{
        unsigned long size;

        /*
         * get geometry: we have to fake one...  trim the size to a
         * multiple of 64 (32k): tell we have 16 sectors, 4 heads,
         * whatever cylinders. Tell also that data starts at sector. 4.
         */
        size = (xpram_pages * 8) & ~0x3f;
        geo->cylinders = size >> 6;
        geo->heads = 4;
        geo->sectors = 16;
        geo->start = 4;
        return 0;
}

static const struct block_device_operations xpram_devops =
{
        .owner  = THIS_MODULE,
        .submit_bio = xpram_submit_bio,
        .getgeo = xpram_getgeo,
};

/*
 * Setup xpram_sizes array.
 */
static int __init xpram_setup_sizes(unsigned long pages)
{
        unsigned long mem_needed;
        unsigned long mem_auto;
        unsigned long long size;
        char *sizes_end;
        int mem_auto_no;
        int i;

        /* Check number of devices. */
        if (devs <= 0 || devs > XPRAM_MAX_DEVS) {
                pr_err("%d is not a valid number of XPRAM devices\n",devs);
                return -EINVAL;
        }
        xpram_devs = devs;

        /*
         * Copy sizes array to xpram_sizes and align partition
         * sizes to page boundary.
         */
        mem_needed = 0;
        mem_auto_no = 0;
        for (i = 0; i < xpram_devs; i++) {
                if (sizes[i]) {
                        size = simple_strtoull(sizes[i], &sizes_end, 0);
                        switch (*sizes_end) {
                        case 'g':
                        case 'G':
                                size <<= 20;
                                break;
                        case 'm':
                        case 'M':
                                size <<= 10;
                        }
                        xpram_sizes[i] = (size + 3) & -4UL;
                }
                if (xpram_sizes[i])
                        mem_needed += xpram_sizes[i];
                else
                        mem_auto_no++;
        }
        
        pr_info("  number of devices (partitions): %d \n", xpram_devs);
        for (i = 0; i < xpram_devs; i++) {
                if (xpram_sizes[i])
                        pr_info("  size of partition %d: %u kB\n",
                                i, xpram_sizes[i]);
                else
                        pr_info("  size of partition %d to be set "
                                "automatically\n",i);
        }
        pr_info("  memory needed (for sized partitions): %lu kB\n",
                mem_needed);
        pr_info("  partitions to be sized automatically: %d\n",
                mem_auto_no);

        if (mem_needed > pages * 4) {
                pr_err("Not enough expanded memory available\n");
                return -EINVAL;
        }

        /*
         * partitioning:
         * xpram_sizes[i] != 0; partition i has size xpram_sizes[i] kB
         * else:             ; all partitions with zero xpram_sizes[i]
         *                     partition equally the remaining space
         */
        if (mem_auto_no) {
                mem_auto = ((pages - mem_needed / 4) / mem_auto_no) * 4;
                pr_info("  automatically determined "
                        "partition size: %lu kB\n", mem_auto);
                for (i = 0; i < xpram_devs; i++)
                        if (xpram_sizes[i] == 0)
                                xpram_sizes[i] = mem_auto;
        }
        return 0;
}

static int __init xpram_setup_blkdev(void)
{
        unsigned long offset;
        int i, rc = -ENOMEM;

        for (i = 0; i < xpram_devs; i++) {
                xpram_disks[i] = blk_alloc_disk(NUMA_NO_NODE);
                if (!xpram_disks[i])
                        goto out;
                blk_queue_flag_set(QUEUE_FLAG_NONROT, xpram_disks[i]->queue);
                blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM,
                                xpram_disks[i]->queue);
                blk_queue_logical_block_size(xpram_disks[i]->queue, 4096);
        }

        /*
         * Register xpram major.
         */
        rc = register_blkdev(XPRAM_MAJOR, XPRAM_NAME);
        if (rc < 0)
                goto out;

        /*
         * Setup device structures.
         */
        offset = 0;
        for (i = 0; i < xpram_devs; i++) {
                struct gendisk *disk = xpram_disks[i];

                xpram_devices[i].size = xpram_sizes[i] / 4;
                xpram_devices[i].offset = offset;
                offset += xpram_devices[i].size;
                disk->major = XPRAM_MAJOR;
                disk->first_minor = i;
                disk->minors = 1;
                disk->fops = &xpram_devops;
                disk->private_data = &xpram_devices[i];
                sprintf(disk->disk_name, "slram%d", i);
                set_capacity(disk, xpram_sizes[i] << 1);
                add_disk(disk);
        }

        return 0;
out:
        while (i--)
                blk_cleanup_disk(xpram_disks[i]);
        return rc;
}

/*
 * Finally, the init/exit functions.
 */
static void __exit xpram_exit(void)
{
        int i;
        for (i = 0; i < xpram_devs; i++) {
                del_gendisk(xpram_disks[i]);
                blk_cleanup_disk(xpram_disks[i]);
        }
        unregister_blkdev(XPRAM_MAJOR, XPRAM_NAME);
}

static int __init xpram_init(void)
{
        int rc;

        /* Find out size of expanded memory. */
        if (xpram_present() != 0) {
                pr_err("No expanded memory available\n");
                return -ENODEV;
        }
        xpram_pages = xpram_highest_page_index() + 1;
        pr_info("  %u pages expanded memory found (%lu KB).\n",
                xpram_pages, (unsigned long) xpram_pages*4);
        rc = xpram_setup_sizes(xpram_pages);
        if (rc)
                return rc;
        return xpram_setup_blkdev();
}

module_init(xpram_init);
module_exit(xpram_exit);