// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) ????           Jochen Schäuble <psionic@psionic.de>
 * Copyright (c) 2003-2004      Joern Engel <joern@wh.fh-wedel.de>
 *
 * Usage:
 *
 * one commend line parameter per device, each in the form:
 *   phram=<name>,<start>,<len>[,<erasesize>]
 * <name> may be up to 63 characters.
 * <start>, <len>, and <erasesize> can be octal, decimal or hexadecimal.  If followed
 * by "ki", "Mi" or "Gi", the numbers will be interpreted as kilo, mega or
 * gigabytes. <erasesize> is optional and defaults to PAGE_SIZE.
 *
 * Example:
 *      phram=swap,64Mi,128Mi phram=test,900Mi,1Mi,64Ki
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/io.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/mtd/mtd.h>
#include <asm/div64.h>

struct phram_mtd_list {
        struct mtd_info mtd;
        struct list_head list;
};

static LIST_HEAD(phram_list);

static int phram_erase(struct mtd_info *mtd, struct erase_info *instr)
{
        u_char *start = mtd->priv;

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

        return 0;
}

static int phram_point(struct mtd_info *mtd, loff_t from, size_t len,
                size_t *retlen, void **virt, resource_size_t *phys)
{
        *virt = mtd->priv + from;
        *retlen = len;
        return 0;
}

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

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

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

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

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

static void unregister_devices(void)
{
        struct phram_mtd_list *this, *safe;

        list_for_each_entry_safe(this, safe, &phram_list, list) {
                mtd_device_unregister(&this->mtd);
                iounmap(this->mtd.priv);
                kfree(this->mtd.name);
                kfree(this);
        }
}

static int register_device(char *name, phys_addr_t start, size_t len, uint32_t erasesize)
{
        struct phram_mtd_list *new;
        int ret = -ENOMEM;

        new = kzalloc(sizeof(*new), GFP_KERNEL);
        if (!new)
                goto out0;

        ret = -EIO;
        new->mtd.priv = ioremap(start, len);
        if (!new->mtd.priv) {
                pr_err("ioremap failed\n");
                goto out1;
        }


        new->mtd.name = name;
        new->mtd.size = len;
        new->mtd.flags = MTD_CAP_RAM;
        new->mtd._erase = phram_erase;
        new->mtd._point = phram_point;
        new->mtd._unpoint = phram_unpoint;
        new->mtd._read = phram_read;
        new->mtd._write = phram_write;
        new->mtd.owner = THIS_MODULE;
        new->mtd.type = MTD_RAM;
        new->mtd.erasesize = erasesize;
        new->mtd.writesize = 1;

        ret = -EAGAIN;
        if (mtd_device_register(&new->mtd, NULL, 0)) {
                pr_err("Failed to register new device\n");
                goto out2;
        }

        list_add_tail(&new->list, &phram_list);
        return 0;

out2:
        iounmap(new->mtd.priv);
out1:
        kfree(new);
out0:
        return ret;
}

static int parse_num64(uint64_t *num64, char *token)
{
        size_t len;
        int shift = 0;
        int ret;

        len = strlen(token);
        /* By dwmw2 editorial decree, "ki", "Mi" or "Gi" are to be used. */
        if (len > 2) {
                if (token[len - 1] == 'i') {
                        switch (token[len - 2]) {
                        case 'G':
                                shift += 10;
                                fallthrough;
                        case 'M':
                                shift += 10;
                                fallthrough;
                        case 'k':
                                shift += 10;
                                token[len - 2] = 0;
                                break;
                        default:
                                return -EINVAL;
                        }
                }
        }

        ret = kstrtou64(token, 0, num64);
        *num64 <<= shift;

        return ret;
}

static int parse_name(char **pname, const char *token)
{
        size_t len;
        char *name;

        len = strlen(token) + 1;
        if (len > 64)
                return -ENOSPC;

        name = kstrdup(token, GFP_KERNEL);
        if (!name)
                return -ENOMEM;

        *pname = name;
        return 0;
}


static inline void kill_final_newline(char *str)
{
        char *newline = strrchr(str, '\n');

        if (newline && !newline[1])
                *newline = 0;
}


#define parse_err(fmt, args...) do {    \
        pr_err(fmt , ## args);  \
        return 1;               \
} while (0)

#ifndef MODULE
static int phram_init_called;
/*
 * This shall contain the module parameter if any. It is of the form:
 * - phram=<device>,<address>,<size>[,<erasesize>] for module case
 * - phram.phram=<device>,<address>,<size>[,<erasesize>] for built-in case
 * We leave 64 bytes for the device name, 20 for the address , 20 for the
 * size and 20 for the erasesize.
 * Example: phram.phram=rootfs,0xa0000000,512Mi,65536
 */
static char phram_paramline[64 + 20 + 20 + 20];
#endif

static int phram_setup(const char *val)
{
        char buf[64 + 20 + 20 + 20], *str = buf;
        char *token[4];
        char *name;
        uint64_t start;
        uint64_t len;
        uint64_t erasesize = PAGE_SIZE;
        uint32_t rem;
        int i, ret;

        if (strnlen(val, sizeof(buf)) >= sizeof(buf))
                parse_err("parameter too long\n");

        strcpy(str, val);
        kill_final_newline(str);

        for (i = 0; i < 4; i++)
                token[i] = strsep(&str, ",");

        if (str)
                parse_err("too many arguments\n");

        if (!token[2])
                parse_err("not enough arguments\n");

        ret = parse_name(&name, token[0]);
        if (ret)
                return ret;

        ret = parse_num64(&start, token[1]);
        if (ret) {
                parse_err("illegal start address\n");
                goto error;
        }

        ret = parse_num64(&len, token[2]);
        if (ret) {
                parse_err("illegal device length\n");
                goto error;
        }

        if (token[3]) {
                ret = parse_num64(&erasesize, token[3]);
                if (ret) {
                        parse_err("illegal erasesize\n");
                        goto error;
                }
        }

        if (erasesize)
                div_u64_rem(len, (uint32_t)erasesize, &rem);

        if (len == 0 || erasesize == 0 || erasesize > len
            || erasesize > UINT_MAX || rem) {
                parse_err("illegal erasesize or len\n");
                ret = -EINVAL;
                goto error;
        }

        ret = register_device(name, start, len, (uint32_t)erasesize);
        if (ret)
                goto error;

        pr_info("%s device: %#llx at %#llx for erasesize %#llx\n", name, len, start, erasesize);
        return 0;

error:
        kfree(name);
        return ret;
}

static int phram_param_call(const char *val, const struct kernel_param *kp)
{
#ifdef MODULE
        return phram_setup(val);
#else
        /*
         * If more parameters are later passed in via
         * /sys/module/phram/parameters/phram
         * and init_phram() has already been called,
         * we can parse the argument now.
         */

        if (phram_init_called)
                return phram_setup(val);

        /*
         * During early boot stage, we only save the parameters
         * here. We must parse them later: if the param passed
         * from kernel boot command line, phram_param_call() is
         * called so early that it is not possible to resolve
         * the device (even kmalloc() fails). Defer that work to
         * phram_setup().
         */

        if (strlen(val) >= sizeof(phram_paramline))
                return -ENOSPC;
        strcpy(phram_paramline, val);

        return 0;
#endif
}

module_param_call(phram, phram_param_call, NULL, NULL, 0200);
MODULE_PARM_DESC(phram, "Memory region to map. \"phram=<name>,<start>,<length>[,<erasesize>]\"");


static int __init init_phram(void)
{
        int ret = 0;

#ifndef MODULE
        if (phram_paramline[0])
                ret = phram_setup(phram_paramline);
        phram_init_called = 1;
#endif

        return ret;
}

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

module_init(init_phram);
module_exit(cleanup_phram);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Joern Engel <joern@wh.fh-wedel.de>");
MODULE_DESCRIPTION("MTD driver for physical RAM");