// SPDX-License-Identifier: GPL-2.0-only
/*======================================================================

  This driver provides a method to access memory not used by the kernel
  itself (i.e. if the kernel commandline mem=xxx is used). To actually
  use slram at least mtdblock or mtdchar is required (for block or
  character device access).

  Usage:

  if compiled as loadable module:
    modprobe slram map=<name>,<start>,<end/offset>
  if statically linked into the kernel use the following kernel cmd.line
    slram=<name>,<start>,<end/offset>

  <name>: name of the device that will be listed in /proc/mtd
  <start>: start of the memory region, decimal or hex (0xabcdef)
  <end/offset>: end of the memory region. It's possible to use +0x1234
                to specify the offset instead of the absolute address

  NOTE:
  With slram it's only possible to map a contiguous memory region. Therefore
  if there's a device mapped somewhere in the region specified slram will
  fail to load (see kernel log if modprobe fails).

  -

  Jochen Schaeuble <psionic@psionic.de>

======================================================================*/


#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/ptrace.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/timer.h>
#include <linux/major.h>
#include <linux/fs.h>
#include <linux/ioctl.h>
#include <linux/init.h>
#include <linux/io.h>

#include <linux/mtd/mtd.h>

#define SLRAM_MAX_DEVICES_PARAMS 6              /* 3 parameters / device */
#define SLRAM_BLK_SZ 0x4000

#define T(fmt, args...) printk(KERN_DEBUG fmt, ## args)
#define E(fmt, args...) printk(KERN_NOTICE fmt, ## args)

typedef struct slram_priv {
        u_char *start;
        u_char *end;
} slram_priv_t;

typedef struct slram_mtd_list {
        struct mtd_info *mtdinfo;
        struct slram_mtd_list *next;
} slram_mtd_list_t;

#ifdef MODULE
static char *map[SLRAM_MAX_DEVICES_PARAMS];

module_param_array(map, charp, NULL, 0);
MODULE_PARM_DESC(map, "List of memory regions to map. \"map=<name>, <start>, <length / end>\"");
#else
static char *map;
#endif

static slram_mtd_list_t *slram_mtdlist = NULL;

static int slram_erase(struct mtd_info *, struct erase_info *);
static int slram_point(struct mtd_info *, loff_t, size_t, size_t *, void **,
                resource_size_t *);
static int slram_unpoint(struct mtd_info *, loff_t, size_t);
static int slram_read(struct mtd_info *, loff_t, size_t, size_t *, u_char *);
static int slram_write(struct mtd_info *, loff_t, size_t, size_t *, const u_char *);

static int slram_erase(struct mtd_info *mtd, struct erase_info *instr)
{
        slram_priv_t *priv = mtd->priv;

        memset(priv->start + instr->addr, 0xff, instr->len);

        return(0);
}

static int slram_point(struct mtd_info *mtd, loff_t from, size_t len,
                size_t *retlen, void **virt, resource_size_t *phys)
{
        slram_priv_t *priv = mtd->priv;

        *virt = priv->start + from;
        *retlen = len;
        return(0);
}

static int slram_unpoint(struct mtd_info *mtd, loff_t from, size_t len)
{
        return 0;
}

static int slram_read(struct mtd_info *mtd, loff_t from, size_t len,
                size_t *retlen, u_char *buf)
{
        slram_priv_t *priv = mtd->priv;

        memcpy(buf, priv->start + from, len);
        *retlen = len;
        return(0);
}

static int slram_write(struct mtd_info *mtd, loff_t to, size_t len,
                size_t *retlen, const u_char *buf)
{
        slram_priv_t *priv = mtd->priv;

        memcpy(priv->start + to, buf, len);
        *retlen = len;
        return(0);
}

/*====================================================================*/

static int register_device(char *name, unsigned long start, unsigned long length)
{
        slram_mtd_list_t **curmtd;

        curmtd = &slram_mtdlist;
        while (*curmtd) {
                curmtd = &(*curmtd)->next;
        }

        *curmtd = kmalloc_obj(slram_mtd_list_t);
        if (!(*curmtd)) {
                E("slram: Cannot allocate new MTD device.\n");
                return(-ENOMEM);
        }
        (*curmtd)->mtdinfo = kzalloc_obj(struct mtd_info);
        (*curmtd)->next = NULL;

        if ((*curmtd)->mtdinfo) {
                (*curmtd)->mtdinfo->priv =
                        kzalloc_obj(slram_priv_t);

                if (!(*curmtd)->mtdinfo->priv) {
                        kfree((*curmtd)->mtdinfo);
                        (*curmtd)->mtdinfo = NULL;
                }
        }

        if (!(*curmtd)->mtdinfo) {
                E("slram: Cannot allocate new MTD device.\n");
                return(-ENOMEM);
        }

        if (!(((slram_priv_t *)(*curmtd)->mtdinfo->priv)->start =
                memremap(start, length,
                         MEMREMAP_WB | MEMREMAP_WT | MEMREMAP_WC))) {
                E("slram: memremap failed\n");
                return -EIO;
        }
        ((slram_priv_t *)(*curmtd)->mtdinfo->priv)->end =
                ((slram_priv_t *)(*curmtd)->mtdinfo->priv)->start + length;


        (*curmtd)->mtdinfo->name = name;
        (*curmtd)->mtdinfo->size = length;
        (*curmtd)->mtdinfo->flags = MTD_CAP_RAM;
        (*curmtd)->mtdinfo->_erase = slram_erase;
        (*curmtd)->mtdinfo->_point = slram_point;
        (*curmtd)->mtdinfo->_unpoint = slram_unpoint;
        (*curmtd)->mtdinfo->_read = slram_read;
        (*curmtd)->mtdinfo->_write = slram_write;
        (*curmtd)->mtdinfo->owner = THIS_MODULE;
        (*curmtd)->mtdinfo->type = MTD_RAM;
        (*curmtd)->mtdinfo->erasesize = SLRAM_BLK_SZ;
        (*curmtd)->mtdinfo->writesize = 1;

        if (mtd_device_register((*curmtd)->mtdinfo, NULL, 0))   {
                E("slram: Failed to register new device\n");
                memunmap(((slram_priv_t *)(*curmtd)->mtdinfo->priv)->start);
                kfree((*curmtd)->mtdinfo->priv);
                kfree((*curmtd)->mtdinfo);
                return(-EAGAIN);
        }
        T("slram: Registered device %s from %luKiB to %luKiB\n", name,
                        (start / 1024), ((start + length) / 1024));
        T("slram: Mapped from 0x%p to 0x%p\n",
                        ((slram_priv_t *)(*curmtd)->mtdinfo->priv)->start,
                        ((slram_priv_t *)(*curmtd)->mtdinfo->priv)->end);
        return(0);
}

static void unregister_devices(void)
{
        slram_mtd_list_t *nextitem;

        while (slram_mtdlist) {
                nextitem = slram_mtdlist->next;
                mtd_device_unregister(slram_mtdlist->mtdinfo);
                memunmap(((slram_priv_t *)slram_mtdlist->mtdinfo->priv)->start);
                kfree(slram_mtdlist->mtdinfo->priv);
                kfree(slram_mtdlist->mtdinfo);
                kfree(slram_mtdlist);
                slram_mtdlist = nextitem;
        }
}

static unsigned long handle_unit(unsigned long value, char *unit)
{
        if ((*unit == 'M') || (*unit == 'm')) {
                return(value * 1024 * 1024);
        } else if ((*unit == 'K') || (*unit == 'k')) {
                return(value * 1024);
        }
        return(value);
}

static int parse_cmdline(char *devname, char *szstart, char *szlength)
{
        char *buffer;
        unsigned long devstart;
        unsigned long devlength;

        if ((!devname) || (!szstart) || (!szlength)) {
                unregister_devices();
                return(-EINVAL);
        }

        devstart = simple_strtoul(szstart, &buffer, 0);
        devstart = handle_unit(devstart, buffer);

        if (*(szlength) != '+') {
                devlength = simple_strtoul(szlength, &buffer, 0);
                devlength = handle_unit(devlength, buffer);
                if (devlength < devstart)
                        goto err_out;

                devlength -= devstart;
        } else {
                devlength = simple_strtoul(szlength + 1, &buffer, 0);
                devlength = handle_unit(devlength, buffer);
        }
        T("slram: devname=%s, devstart=0x%lx, devlength=0x%lx\n",
                        devname, devstart, devlength);
        if (devlength % SLRAM_BLK_SZ != 0)
                goto err_out;

        if ((devstart = register_device(devname, devstart, devlength))){
                unregister_devices();
                return((int)devstart);
        }
        return(0);

err_out:
        E("slram: Illegal length parameter.\n");
        return(-EINVAL);
}

#ifndef MODULE

static int __init mtd_slram_setup(char *str)
{
        map = str;
        return(1);
}

__setup("slram=", mtd_slram_setup);

#endif

static int __init init_slram(void)
{
        char *devname;

#ifndef MODULE
        char *devstart;
        char *devlength;

        if (!map) {
                E("slram: not enough parameters.\n");
                return(-EINVAL);
        }
        while (map) {
                devname = devstart = devlength = NULL;

                if (!(devname = strsep(&map, ","))) {
                        E("slram: No devicename specified.\n");
                        break;
                }
                T("slram: devname = %s\n", devname);
                if ((!map) || (!(devstart = strsep(&map, ",")))) {
                        E("slram: No devicestart specified.\n");
                        break;
                }
                T("slram: devstart = %s\n", devstart);
                if ((!map) || (!(devlength = strsep(&map, ",")))) {
                        E("slram: No devicelength / -end specified.\n");
                        break;
                }
                T("slram: devlength = %s\n", devlength);
                if (parse_cmdline(devname, devstart, devlength) != 0) {
                        return(-EINVAL);
                }
        }
#else
        int count;
        int i;

        for (count = 0; count < SLRAM_MAX_DEVICES_PARAMS && map[count];
                        count++) {
        }

        if ((count % 3 != 0) || (count == 0)) {
                E("slram: not enough parameters.\n");
                return(-EINVAL);
        }
        for (i = 0; i < (count / 3); i++) {
                devname = map[i * 3];

                if (parse_cmdline(devname, map[i * 3 + 1], map[i * 3 + 2])!=0) {
                        return(-EINVAL);
                }

        }
#endif /* !MODULE */

        return(0);
}

static void __exit cleanup_slram(void)
{
        unregister_devices();
}

module_init(init_slram);
module_exit(cleanup_slram);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Jochen Schaeuble <psionic@psionic.de>");
MODULE_DESCRIPTION("MTD driver for uncached system RAM");