// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2022 Rafał Miłecki <rafal@milecki.pl>
 */

#include <linux/crc32.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/mtd/mtd.h>
#include <linux/nvmem-consumer.h>
#include <linux/nvmem-provider.h>
#include <linux/of_device.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

enum u_boot_env_format {
	U_BOOT_FORMAT_SINGLE,
	U_BOOT_FORMAT_REDUNDANT,
};

struct u_boot_env {
	struct device *dev;
	enum u_boot_env_format format;

	struct mtd_info *mtd;

	/* Cells */
	struct nvmem_cell_info *cells;
	int ncells;
};

struct u_boot_env_image_single {
	__le32 crc32;
	uint8_t data[];
} __packed;

struct u_boot_env_image_redundant {
	__le32 crc32;
	u8 mark;
	uint8_t data[];
} __packed;

static int u_boot_env_read(void *context, unsigned int offset, void *val,
			   size_t bytes)
{
	struct u_boot_env *priv = context;
	struct device *dev = priv->dev;
	size_t bytes_read;
	int err;

	err = mtd_read(priv->mtd, offset, bytes, &bytes_read, val);
	if (err && !mtd_is_bitflip(err)) {
		dev_err(dev, "Failed to read from mtd: %d\n", err);
		return err;
	}

	if (bytes_read != bytes) {
		dev_err(dev, "Failed to read %zu bytes\n", bytes);
		return -EIO;
	}

	return 0;
}

static int u_boot_env_add_cells(struct u_boot_env *priv, uint8_t *buf,
				size_t data_offset, size_t data_len)
{
	struct device *dev = priv->dev;
	char *data = buf + data_offset;
	char *var, *value, *eq;
	int idx;

	priv->ncells = 0;
	for (var = data; var < data + data_len && *var; var += strlen(var) + 1)
		priv->ncells++;

	priv->cells = devm_kcalloc(dev, priv->ncells, sizeof(*priv->cells), GFP_KERNEL);
	if (!priv->cells)
		return -ENOMEM;

	for (var = data, idx = 0;
	     var < data + data_len && *var;
	     var = value + strlen(value) + 1, idx++) {
		eq = strchr(var, '=');
		if (!eq)
			break;
		*eq = '\0';
		value = eq + 1;

		priv->cells[idx].name = devm_kstrdup(dev, var, GFP_KERNEL);
		if (!priv->cells[idx].name)
			return -ENOMEM;
		priv->cells[idx].offset = data_offset + value - data;
		priv->cells[idx].bytes = strlen(value);
		priv->cells[idx].np = of_get_child_by_name(dev->of_node, priv->cells[idx].name);
	}

	if (WARN_ON(idx != priv->ncells))
		priv->ncells = idx;

	return 0;
}

static int u_boot_env_parse(struct u_boot_env *priv)
{
	struct device *dev = priv->dev;
	size_t crc32_data_offset;
	size_t crc32_data_len;
	size_t crc32_offset;
	size_t data_offset;
	size_t data_len;
	uint32_t crc32;
	uint32_t calc;
	size_t bytes;
	uint8_t *buf;
	int err;

	buf = kcalloc(1, priv->mtd->size, GFP_KERNEL);
	if (!buf) {
		err = -ENOMEM;
		goto err_out;
	}

	err = mtd_read(priv->mtd, 0, priv->mtd->size, &bytes, buf);
	if ((err && !mtd_is_bitflip(err)) || bytes != priv->mtd->size) {
		dev_err(dev, "Failed to read from mtd: %d\n", err);
		goto err_kfree;
	}

	switch (priv->format) {
	case U_BOOT_FORMAT_SINGLE:
		crc32_offset = offsetof(struct u_boot_env_image_single, crc32);
		crc32_data_offset = offsetof(struct u_boot_env_image_single, data);
		data_offset = offsetof(struct u_boot_env_image_single, data);
		break;
	case U_BOOT_FORMAT_REDUNDANT:
		crc32_offset = offsetof(struct u_boot_env_image_redundant, crc32);
		crc32_data_offset = offsetof(struct u_boot_env_image_redundant, data);
		data_offset = offsetof(struct u_boot_env_image_redundant, data);
		break;
	}
	crc32 = le32_to_cpu(*(__le32 *)(buf + crc32_offset));
	crc32_data_len = priv->mtd->size - crc32_data_offset;
	data_len = priv->mtd->size - data_offset;

	calc = crc32(~0, buf + crc32_data_offset, crc32_data_len) ^ ~0L;
	if (calc != crc32) {
		dev_err(dev, "Invalid calculated CRC32: 0x%08x (expected: 0x%08x)\n", calc, crc32);
		err = -EINVAL;
		goto err_kfree;
	}

	buf[priv->mtd->size - 1] = '\0';
	err = u_boot_env_add_cells(priv, buf, data_offset, data_len);
	if (err)
		dev_err(dev, "Failed to add cells: %d\n", err);

err_kfree:
	kfree(buf);
err_out:
	return err;
}

static int u_boot_env_probe(struct platform_device *pdev)
{
	struct nvmem_config config = {
		.name = "u-boot-env",
		.reg_read = u_boot_env_read,
	};
	struct device *dev = &pdev->dev;
	struct device_node *np = dev->of_node;
	struct u_boot_env *priv;
	int err;

	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
	if (!priv)
		return -ENOMEM;
	priv->dev = dev;

	priv->format = (uintptr_t)of_device_get_match_data(dev);

	priv->mtd = of_get_mtd_device_by_node(np);
	if (IS_ERR(priv->mtd)) {
		dev_err_probe(dev, PTR_ERR(priv->mtd), "Failed to get %pOF MTD\n", np);
		return PTR_ERR(priv->mtd);
	}

	err = u_boot_env_parse(priv);
	if (err)
		return err;

	config.dev = dev;
	config.cells = priv->cells;
	config.ncells = priv->ncells;
	config.priv = priv;
	config.size = priv->mtd->size;

	return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
}

static const struct of_device_id u_boot_env_of_match_table[] = {
	{ .compatible = "u-boot,env", .data = (void *)U_BOOT_FORMAT_SINGLE, },
	{ .compatible = "u-boot,env-redundant-bool", .data = (void *)U_BOOT_FORMAT_REDUNDANT, },
	{ .compatible = "u-boot,env-redundant-count", .data = (void *)U_BOOT_FORMAT_REDUNDANT, },
	{},
};

static struct platform_driver u_boot_env_driver = {
	.probe = u_boot_env_probe,
	.driver = {
		.name = "u_boot_env",
		.of_match_table = u_boot_env_of_match_table,
	},
};
module_platform_driver(u_boot_env_driver);

MODULE_AUTHOR("Rafał Miłecki");
MODULE_LICENSE("GPL");
MODULE_DEVICE_TABLE(of, u_boot_env_of_match_table);