nvmem: add driver handling U-Boot environment variables

U-Boot binary contains a block of environment variables (NVMEM) that
should be parsed and exposed as NVMEM cells.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

MAINTAINERS

@@ -19402,6 +19402,7 @@ U-BOOT ENVIRONMENT VARIABLES
 M:	Rafał Miłecki <rafal@milecki.pl>
 S:	Maintained
 F:	Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
+F:	drivers/nvmem/u-boot-env.c
 
 UACCE ACCELERATOR FRAMEWORK
 M:	Zhangfei Gao <zhangfei.gao@linaro.org>

drivers/nvmem/Kconfig

@@ -300,4 +300,14 @@ config NVMEM_BRCM_NVRAM
 	  This driver provides support for Broadcom's NVRAM that can be accessed
 	  using I/O mapping.
 
+config NVMEM_U_BOOT_ENV
+	tristate "U-Boot environment variables support"
+	depends on ARCH_BCM4908 || COMPILE_TEST
+	depends on OF
+	help
+	  This driver adds support for parsing U-Boot environment variables
+	  stored on flash partition.
+
+	  If compiled as module it will be called nvmem_u-boot-env.
+
 endif

drivers/nvmem/Makefile

@@ -61,3 +61,5 @@ obj-$(CONFIG_NVMEM_RMEM) 	+= nvmem-rmem.o
 nvmem-rmem-y			:= rmem.o
 obj-$(CONFIG_NVMEM_BRCM_NVRAM)	+= nvmem_brcm_nvram.o
 nvmem_brcm_nvram-y		:= brcm_nvram.o
+obj-$(CONFIG_NVMEM_U_BOOT_ENV)	+= nvmem_u-boot-env.o
+nvmem_u-boot-env-y		:= u-boot-env.o

drivers/nvmem/u-boot-env.c

@@ -0,0 +1,235 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 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_DEFAULT,
+	U_BOOT_FORMAT_BRCM,
+};
+
+struct u_boot_env {
+	struct device *dev;
+	enum u_boot_env_format format;
+	struct mtd_info *mtd;
+	size_t offset;
+	size_t size;
+	struct nvmem_cell_info *cells;
+	int ncells;
+};
+
+struct u_boot_env_image {
+	__le32 crc32;
+	uint8_t data[0];
+} __packed;
+
+struct u_boot_brcm_header {
+	__le32 unk;
+	__le32 len;
+} __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, priv->offset + 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 %zd bytes\n", bytes);
+		return err;
+	}
+
+	return 0;
+}
+
+static int u_boot_env_add_cells(struct u_boot_env *priv, size_t data_offset,
+				uint8_t *data, size_t len)
+{
+	struct device *dev = priv->dev;
+	char *var, *value, *eq;
+	int idx;
+
+	priv->ncells = 0;
+	for (var = data; var < (char *)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 < (char *)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 - (char *)data;
+		priv->cells[idx].bytes = strlen(value);
+	}
+
+	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;
+	struct u_boot_env_image *image;
+	size_t image_offset;
+	size_t image_len;
+	uint32_t crc32;
+	size_t bytes;
+	uint8_t *buf;
+	int err;
+
+	image_offset = 0;
+	image_len = priv->size;
+	if (priv->format == U_BOOT_FORMAT_BRCM) {
+		struct u_boot_brcm_header header;
+
+		err = mtd_read(priv->mtd, priv->offset, sizeof(header), &bytes,
+			       (uint8_t *)&header);
+		if (err && !mtd_is_bitflip(err)) {
+			dev_err(dev, "Failed to read from mtd: %d\n", err);
+			return err;
+		}
+
+		image_offset = sizeof(header);
+		image_len = le32_to_cpu(header.len);
+	}
+
+	buf = kcalloc(1, image_len, GFP_KERNEL);
+	if (!buf) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+	image = (struct u_boot_env_image *)buf;
+
+	err = mtd_read(priv->mtd, priv->offset + image_offset, image_len, &bytes, buf);
+	if (err && !mtd_is_bitflip(err)) {
+		dev_err(dev, "Failed to read from mtd: %d\n", err);
+		goto err_kfree;
+	}
+
+	crc32 = crc32(~0, buf + 4, image_len - 4) ^ ~0L;
+	if (crc32 != le32_to_cpu(image->crc32)) {
+		dev_err(dev, "Invalid calculated CRC32: 0x%08x\n", crc32);
+		err = -EINVAL;
+		goto err_kfree;
+	}
+
+	buf[image_len - 1] = '\0';
+	err = u_boot_env_add_cells(priv, image_offset + sizeof(*image),
+				   buf + sizeof(*image),
+				   image_len - sizeof(*image));
+	if (err)
+		dev_err(dev, "Failed to add cells: %d\n", err);
+
+err_kfree:
+	kfree(buf);
+err_out:
+	return err;
+}
+
+static const struct of_device_id u_boot_env_of_match_table[] = {
+	{ .compatible = "u-boot,env", .data = (void *)U_BOOT_FORMAT_DEFAULT, },
+	{ .compatible = "brcm,env", .data = (void *)U_BOOT_FORMAT_BRCM, },
+	{},
+};
+
+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;
+	const struct of_device_id *of_id;
+	struct u_boot_env *priv;
+	const char *label;
+	int err;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+	priv->dev = dev;
+
+	of_id = of_match_device(u_boot_env_of_match_table, dev);
+	if (!of_id)
+		return -EINVAL;
+	priv->format = (uintptr_t)of_id->data;
+
+	if (of_property_read_u32(np, "reg", (u32 *)&priv->offset) ||
+	    of_property_read_u32_index(np, "reg", 1, (u32 *)&priv->size)) {
+		dev_err(dev, "Failed to read \"reg\" property\n");
+		return -EINVAL;
+	}
+
+	label = of_get_property(np->parent, "label", NULL);
+	if (!label)
+		label = np->parent->name;
+
+	priv->mtd = get_mtd_device_nm(label);
+	if (IS_ERR(priv->mtd)) {
+		dev_err(dev, "Failed to find \"%s\" MTD device: %ld\n", label, PTR_ERR(priv->mtd));
+		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->size;
+
+	return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
+}
+
+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,
+	},
+};
+
+static int __init u_boot_env_init(void)
+{
+	return platform_driver_register(&u_boot_env_driver);
+}
+
+subsys_initcall_sync(u_boot_env_init);
+
+MODULE_AUTHOR("Rafał Miłecki");
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(of, u_boot_env_of_match_table);