// SPDX-License-Identifier: GPL-2.0

#define dev_fmt(fmt) "mtdoops-pstore: " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/pstore_blk.h>
#include <linux/mtd/mtd.h>
#include <linux/bitops.h>
#include <linux/slab.h>

static struct mtdpstore_context {
        int index;
        struct pstore_blk_config info;
        struct pstore_device_info dev;
        struct mtd_info *mtd;
        unsigned long *rmmap;           /* removed bit map */
        unsigned long *usedmap;         /* used bit map */
        /*
         * used for panic write
         * As there are no block_isbad for panic case, we should keep this
         * status before panic to ensure panic_write not failed.
         */
        unsigned long *badmap;          /* bad block bit map */
} oops_cxt;

static int mtdpstore_block_isbad(struct mtdpstore_context *cxt, loff_t off)
{
        int ret;
        struct mtd_info *mtd = cxt->mtd;
        u64 blknum;

        off = ALIGN_DOWN(off, mtd->erasesize);
        blknum = div_u64(off, mtd->erasesize);

        if (test_bit(blknum, cxt->badmap))
                return true;
        ret = mtd_block_isbad(mtd, off);
        if (ret < 0) {
                dev_err(&mtd->dev, "mtd_block_isbad failed, aborting\n");
                return ret;
        } else if (ret > 0) {
                set_bit(blknum, cxt->badmap);
                return true;
        }
        return false;
}

static inline int mtdpstore_panic_block_isbad(struct mtdpstore_context *cxt,
                loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        u64 blknum;

        off = ALIGN_DOWN(off, mtd->erasesize);
        blknum = div_u64(off, mtd->erasesize);
        return test_bit(blknum, cxt->badmap);
}

static inline void mtdpstore_mark_used(struct mtdpstore_context *cxt,
                loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        u64 zonenum = div_u64(off, cxt->info.kmsg_size);

        dev_dbg(&mtd->dev, "mark zone %llu used\n", zonenum);
        set_bit(zonenum, cxt->usedmap);
}

static inline void mtdpstore_mark_unused(struct mtdpstore_context *cxt,
                loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        u64 zonenum = div_u64(off, cxt->info.kmsg_size);

        dev_dbg(&mtd->dev, "mark zone %llu unused\n", zonenum);
        clear_bit(zonenum, cxt->usedmap);
}

static inline void mtdpstore_block_mark_unused(struct mtdpstore_context *cxt,
                loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        u32 zonecnt = mtd->erasesize / cxt->info.kmsg_size;
        u64 zonenum;

        off = ALIGN_DOWN(off, mtd->erasesize);
        zonenum = div_u64(off, cxt->info.kmsg_size);
        while (zonecnt > 0) {
                dev_dbg(&mtd->dev, "mark zone %llu unused\n", zonenum);
                clear_bit(zonenum, cxt->usedmap);
                zonenum++;
                zonecnt--;
        }
}

static inline int mtdpstore_is_used(struct mtdpstore_context *cxt, loff_t off)
{
        u64 zonenum = div_u64(off, cxt->info.kmsg_size);
        u64 blknum = div_u64(off, cxt->mtd->erasesize);

        if (test_bit(blknum, cxt->badmap))
                return true;
        return test_bit(zonenum, cxt->usedmap);
}

static int mtdpstore_block_is_used(struct mtdpstore_context *cxt,
                loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        u32 zonecnt = mtd->erasesize / cxt->info.kmsg_size;
        u64 zonenum;

        off = ALIGN_DOWN(off, mtd->erasesize);
        zonenum = div_u64(off, cxt->info.kmsg_size);
        while (zonecnt > 0) {
                if (test_bit(zonenum, cxt->usedmap))
                        return true;
                zonenum++;
                zonecnt--;
        }
        return false;
}

static int mtdpstore_is_empty(struct mtdpstore_context *cxt, char *buf,
                size_t size)
{
        struct mtd_info *mtd = cxt->mtd;
        size_t sz;
        int i;

        sz = min_t(uint32_t, size, mtd->writesize / 4);
        for (i = 0; i < sz; i++) {
                if (buf[i] != (char)0xFF)
                        return false;
        }
        return true;
}

static void mtdpstore_mark_removed(struct mtdpstore_context *cxt, loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        u64 zonenum = div_u64(off, cxt->info.kmsg_size);

        dev_dbg(&mtd->dev, "mark zone %llu removed\n", zonenum);
        set_bit(zonenum, cxt->rmmap);
}

static void mtdpstore_block_clear_removed(struct mtdpstore_context *cxt,
                loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        u32 zonecnt = mtd->erasesize / cxt->info.kmsg_size;
        u64 zonenum;

        off = ALIGN_DOWN(off, mtd->erasesize);
        zonenum = div_u64(off, cxt->info.kmsg_size);
        while (zonecnt > 0) {
                clear_bit(zonenum, cxt->rmmap);
                zonenum++;
                zonecnt--;
        }
}

static int mtdpstore_block_is_removed(struct mtdpstore_context *cxt,
                loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        u32 zonecnt = mtd->erasesize / cxt->info.kmsg_size;
        u64 zonenum;

        off = ALIGN_DOWN(off, mtd->erasesize);
        zonenum = div_u64(off, cxt->info.kmsg_size);
        while (zonecnt > 0) {
                if (test_bit(zonenum, cxt->rmmap))
                        return true;
                zonenum++;
                zonecnt--;
        }
        return false;
}

static int mtdpstore_erase_do(struct mtdpstore_context *cxt, loff_t off)
{
        struct mtd_info *mtd = cxt->mtd;
        struct erase_info erase;
        int ret;

        off = ALIGN_DOWN(off, cxt->mtd->erasesize);
        dev_dbg(&mtd->dev, "try to erase off 0x%llx\n", off);
        erase.len = cxt->mtd->erasesize;
        erase.addr = off;
        ret = mtd_erase(cxt->mtd, &erase);
        if (!ret)
                mtdpstore_block_clear_removed(cxt, off);
        else
                dev_err(&mtd->dev, "erase of region [0x%llx, 0x%llx] on \"%s\" failed\n",
                       (unsigned long long)erase.addr,
                       (unsigned long long)erase.len, cxt->info.device);
        return ret;
}

/*
 * called while removing file
 *
 * Avoiding over erasing, do erase block only when the whole block is unused.
 * If the block contains valid log, do erase lazily on flush_removed() when
 * unregister.
 */
static ssize_t mtdpstore_erase(size_t size, loff_t off)
{
        struct mtdpstore_context *cxt = &oops_cxt;

        if (mtdpstore_block_isbad(cxt, off))
                return -EIO;

        mtdpstore_mark_unused(cxt, off);

        /* If the block still has valid data, mtdpstore do erase lazily */
        if (likely(mtdpstore_block_is_used(cxt, off))) {
                mtdpstore_mark_removed(cxt, off);
                return 0;
        }

        /* all zones are unused, erase it */
        return mtdpstore_erase_do(cxt, off);
}

/*
 * What is security for mtdpstore?
 * As there is no erase for panic case, we should ensure at least one zone
 * is writable. Otherwise, panic write will fail.
 * If zone is used, write operation will return -ENOMSG, which means that
 * pstore/blk will try one by one until gets an empty zone. So, it is not
 * needed to ensure the next zone is empty, but at least one.
 */
static int mtdpstore_security(struct mtdpstore_context *cxt, loff_t off)
{
        int ret = 0, i;
        struct mtd_info *mtd = cxt->mtd;
        u32 zonenum = (u32)div_u64(off, cxt->info.kmsg_size);
        u32 zonecnt = (u32)div_u64(cxt->mtd->size, cxt->info.kmsg_size);
        u32 blkcnt = (u32)div_u64(cxt->mtd->size, cxt->mtd->erasesize);
        u32 erasesize = cxt->mtd->erasesize;

        for (i = 0; i < zonecnt; i++) {
                u32 num = (zonenum + i) % zonecnt;

                /* found empty zone */
                if (!test_bit(num, cxt->usedmap))
                        return 0;
        }

        /* If there is no any empty zone, we have no way but to do erase */
        while (blkcnt--) {
                div64_u64_rem(off + erasesize, cxt->mtd->size, (u64 *)&off);

                if (mtdpstore_block_isbad(cxt, off))
                        continue;

                ret = mtdpstore_erase_do(cxt, off);
                if (!ret) {
                        mtdpstore_block_mark_unused(cxt, off);
                        break;
                }
        }

        if (ret)
                dev_err(&mtd->dev, "all blocks bad!\n");
        dev_dbg(&mtd->dev, "end security\n");
        return ret;
}

static ssize_t mtdpstore_write(const char *buf, size_t size, loff_t off)
{
        struct mtdpstore_context *cxt = &oops_cxt;
        struct mtd_info *mtd = cxt->mtd;
        size_t retlen;
        int ret;

        if (mtdpstore_block_isbad(cxt, off))
                return -ENOMSG;

        /* zone is used, please try next one */
        if (mtdpstore_is_used(cxt, off))
                return -ENOMSG;

        dev_dbg(&mtd->dev, "try to write off 0x%llx size %zu\n", off, size);
        ret = mtd_write(cxt->mtd, off, size, &retlen, (u_char *)buf);
        if (ret < 0 || retlen != size) {
                dev_err(&mtd->dev, "write failure at %lld (%zu of %zu written), err %d\n",
                                off, retlen, size, ret);
                return -EIO;
        }
        mtdpstore_mark_used(cxt, off);

        mtdpstore_security(cxt, off);
        return retlen;
}

static inline bool mtdpstore_is_io_error(int ret)
{
        return ret < 0 && !mtd_is_bitflip(ret) && !mtd_is_eccerr(ret);
}

/*
 * All zones will be read as pstore/blk will read zone one by one when do
 * recover.
 */
static ssize_t mtdpstore_read(char *buf, size_t size, loff_t off)
{
        struct mtdpstore_context *cxt = &oops_cxt;
        struct mtd_info *mtd = cxt->mtd;
        size_t retlen, done;
        int ret;

        if (mtdpstore_block_isbad(cxt, off))
                return -ENOMSG;

        dev_dbg(&mtd->dev, "try to read off 0x%llx size %zu\n", off, size);
        for (done = 0, retlen = 0; done < size; done += retlen) {
                retlen = 0;

                ret = mtd_read(cxt->mtd, off + done, size - done, &retlen,
                                (u_char *)buf + done);
                if (mtdpstore_is_io_error(ret)) {
                        dev_err(&mtd->dev, "read failure at %lld (%zu of %zu read), err %d\n",
                                        off + done, retlen, size - done, ret);
                        /* the zone may be broken, try next one */
                        return -ENOMSG;
                }

                /*
                 * ECC error. The impact on log data is so small. Maybe we can
                 * still read it and try to understand. So mtdpstore just hands
                 * over what it gets and user can judge whether the data is
                 * valid or not.
                 */
                if (mtd_is_eccerr(ret)) {
                        dev_err(&mtd->dev, "ecc error at %lld (%zu of %zu read), err %d\n",
                                        off + done, retlen, size - done, ret);
                        /* driver may not set retlen when ecc error */
                        retlen = retlen == 0 ? size - done : retlen;
                }
        }

        if (mtdpstore_is_empty(cxt, buf, size))
                mtdpstore_mark_unused(cxt, off);
        else
                mtdpstore_mark_used(cxt, off);

        mtdpstore_security(cxt, off);
        return retlen;
}

static ssize_t mtdpstore_panic_write(const char *buf, size_t size, loff_t off)
{
        struct mtdpstore_context *cxt = &oops_cxt;
        struct mtd_info *mtd = cxt->mtd;
        size_t retlen;
        int ret;

        if (mtdpstore_panic_block_isbad(cxt, off))
                return -ENOMSG;

        /* zone is used, please try next one */
        if (mtdpstore_is_used(cxt, off))
                return -ENOMSG;

        ret = mtd_panic_write(cxt->mtd, off, size, &retlen, (u_char *)buf);
        if (ret < 0 || size != retlen) {
                dev_err(&mtd->dev, "panic write failure at %lld (%zu of %zu read), err %d\n",
                                off, retlen, size, ret);
                return -EIO;
        }
        mtdpstore_mark_used(cxt, off);

        return retlen;
}

static void mtdpstore_notify_add(struct mtd_info *mtd)
{
        int ret;
        struct mtdpstore_context *cxt = &oops_cxt;
        struct pstore_blk_config *info = &cxt->info;
        unsigned long longcnt;

        if (!strcmp(mtd->name, info->device))
                cxt->index = mtd->index;

        if (mtd->index != cxt->index || cxt->index < 0)
                return;

        dev_dbg(&mtd->dev, "found matching MTD device %s\n", mtd->name);

        if (mtd->size < info->kmsg_size * 2) {
                dev_err(&mtd->dev, "MTD partition %d not big enough\n",
                                mtd->index);
                return;
        }
        /*
         * kmsg_size must be aligned to 4096 Bytes, which is limited by
         * psblk. The default value of kmsg_size is 64KB. If kmsg_size
         * is larger than erasesize, some errors will occur since mtdpstore
         * is designed on it.
         */
        if (mtd->erasesize < info->kmsg_size) {
                dev_err(&mtd->dev, "eraseblock size of MTD partition %d too small\n",
                                mtd->index);
                return;
        }
        if (unlikely(info->kmsg_size % mtd->writesize)) {
                dev_err(&mtd->dev, "record size %lu KB must align to write size %d KB\n",
                                info->kmsg_size / 1024,
                                mtd->writesize / 1024);
                return;
        }

        longcnt = BITS_TO_LONGS(div_u64(mtd->size, info->kmsg_size));
        cxt->rmmap = devm_kcalloc(&mtd->dev, longcnt, sizeof(long), GFP_KERNEL);
        cxt->usedmap = devm_kcalloc(&mtd->dev, longcnt, sizeof(long), GFP_KERNEL);

        longcnt = BITS_TO_LONGS(div_u64(mtd->size, mtd->erasesize));
        cxt->badmap = devm_kcalloc(&mtd->dev, longcnt, sizeof(long), GFP_KERNEL);

        if (!cxt->rmmap || !cxt->usedmap || !cxt->badmap)
                return;

        /* just support dmesg right now */
        cxt->dev.flags = PSTORE_FLAGS_DMESG;
        cxt->dev.zone.read = mtdpstore_read;
        cxt->dev.zone.write = mtdpstore_write;
        cxt->dev.zone.erase = mtdpstore_erase;
        cxt->dev.zone.panic_write = mtdpstore_panic_write;
        cxt->dev.zone.total_size = mtd->size;

        ret = register_pstore_device(&cxt->dev);
        if (ret) {
                dev_err(&mtd->dev, "mtd%d register to psblk failed\n",
                                mtd->index);
                return;
        }
        cxt->mtd = mtd;
        dev_info(&mtd->dev, "Attached to MTD device %d\n", mtd->index);
}

static int mtdpstore_flush_removed_do(struct mtdpstore_context *cxt,
                loff_t off, size_t size)
{
        struct mtd_info *mtd = cxt->mtd;
        u_char *buf;
        int ret;
        size_t retlen;
        struct erase_info erase;

        buf = kmalloc(mtd->erasesize, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        /* 1st. read to cache */
        ret = mtd_read(mtd, off, mtd->erasesize, &retlen, buf);
        if (mtdpstore_is_io_error(ret))
                goto free;

        /* 2nd. erase block */
        erase.len = mtd->erasesize;
        erase.addr = off;
        ret = mtd_erase(mtd, &erase);
        if (ret)
                goto free;

        /* 3rd. write back */
        while (size) {
                unsigned int zonesize = cxt->info.kmsg_size;

                /* there is valid data on block, write back */
                if (mtdpstore_is_used(cxt, off)) {
                        ret = mtd_write(mtd, off, zonesize, &retlen, buf);
                        if (ret)
                                dev_err(&mtd->dev, "write failure at %lld (%zu of %u written), err %d\n",
                                                off, retlen, zonesize, ret);
                }

                off += zonesize;
                size -= min_t(unsigned int, zonesize, size);
        }

free:
        kfree(buf);
        return ret;
}

/*
 * What does mtdpstore_flush_removed() do?
 * When user remove any log file on pstore filesystem, mtdpstore should do
 * something to ensure log file removed. If the whole block is no longer used,
 * it's nice to erase the block. However if the block still contains valid log,
 * what mtdpstore can do is to erase and write the valid log back.
 */
static int mtdpstore_flush_removed(struct mtdpstore_context *cxt)
{
        struct mtd_info *mtd = cxt->mtd;
        int ret;
        loff_t off;
        u32 blkcnt = (u32)div_u64(mtd->size, mtd->erasesize);

        for (off = 0; blkcnt > 0; blkcnt--, off += mtd->erasesize) {
                ret = mtdpstore_block_isbad(cxt, off);
                if (ret)
                        continue;

                ret = mtdpstore_block_is_removed(cxt, off);
                if (!ret)
                        continue;

                ret = mtdpstore_flush_removed_do(cxt, off, mtd->erasesize);
                if (ret)
                        return ret;
        }
        return 0;
}

static void mtdpstore_notify_remove(struct mtd_info *mtd)
{
        struct mtdpstore_context *cxt = &oops_cxt;

        if (mtd->index != cxt->index || cxt->index < 0)
                return;

        mtdpstore_flush_removed(cxt);

        unregister_pstore_device(&cxt->dev);
        cxt->mtd = NULL;
        cxt->index = -1;
}

static struct mtd_notifier mtdpstore_notifier = {
        .add    = mtdpstore_notify_add,
        .remove = mtdpstore_notify_remove,
};

static int __init mtdpstore_init(void)
{
        int ret;
        struct mtdpstore_context *cxt = &oops_cxt;
        struct pstore_blk_config *info = &cxt->info;

        ret = pstore_blk_get_config(info);
        if (unlikely(ret))
                return ret;

        if (strlen(info->device) == 0) {
                pr_err("mtd device must be supplied (device name is empty)\n");
                return -EINVAL;
        }
        if (!info->kmsg_size) {
                pr_err("no backend enabled (kmsg_size is 0)\n");
                return -EINVAL;
        }

        /* Setup the MTD device to use */
        ret = kstrtoint((char *)info->device, 0, &cxt->index);
        if (ret)
                cxt->index = -1;

        register_mtd_user(&mtdpstore_notifier);
        return 0;
}
module_init(mtdpstore_init);

static void __exit mtdpstore_exit(void)
{
        unregister_mtd_user(&mtdpstore_notifier);
}
module_exit(mtdpstore_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("WeiXiong Liao <liaoweixiong@allwinnertech.com>");
MODULE_DESCRIPTION("MTD backend for pstore/blk");