[PATCH V2] nvmem: add driver handling U-Boot environment variables

["Rafał Miłecki" <zajec5@gmail.com>]

From: Rafał Miłecki <rafal@milecki.pl>

U-Boot stores its setup as environment variables. It's a list of
key-value pairs stored on flash device with a custom header.

This commit adds an NVMEM driver that:
1. Provides NVMEM access to environment vars binary data
2. Extracts variables as NVMEM cells

It can be used for:
1. Accessing env variables from user-space
2. Reading NVMEM cells by Linux drivers

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
V2: Drop ARCH_BCM4908 dependency as there are plenty architectures using
    U-Boot bootloader. Thanks Srinivas.
---
 MAINTAINERS                |   1 +
 drivers/nvmem/Kconfig      |  11 ++
 drivers/nvmem/Makefile     |   2 +
 drivers/nvmem/u-boot-env.c | 236 +++++++++++++++++++++++++++++++++++++
 4 files changed, 250 insertions(+)
 create mode 100644 drivers/nvmem/u-boot-env.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 2869a958f5e4..368e532444d0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20193,6 +20193,7 @@ 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>
diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 967d0084800e..eee3ff668629 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -337,4 +337,15 @@ config NVMEM_APPLE_EFUSES
 	  This driver can also be built as a module. If so, the module will
 	  be called nvmem-apple-efuses.
 
+config NVMEM_U_BOOT_ENV
+	tristate "U-Boot environment variables support"
+	depends on OF && MTD
+	select CRC32
+	help
+	  U-Boot stores its setup as environment variables. This driver adds
+	  support for verifying & exporting such data. It also exposes variables
+	  as NVMEM cells so they can be referenced by other drivers.
+
+	  If compiled as module it will be called nvmem_u-boot-env.
+
 endif
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 00e136a0a123..d201a02a09ec 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -67,3 +67,5 @@ obj-$(CONFIG_NVMEM_SUNPLUS_OCOTP)	+= nvmem_sunplus_ocotp.o
 nvmem_sunplus_ocotp-y		:= sunplus-ocotp.o
 obj-$(CONFIG_NVMEM_APPLE_EFUSES)	+= nvmem-apple-efuses.o
 nvmem-apple-efuses-y 		:= apple-efuses.o
+obj-$(CONFIG_NVMEM_U_BOOT_ENV)	+= nvmem_u-boot-env.o
+nvmem_u-boot-env-y		:= u-boot-env.o
diff --git a/drivers/nvmem/u-boot-env.c b/drivers/nvmem/u-boot-env.c
new file mode 100644
index 000000000000..c7945d7d5750
--- /dev/null
+++ b/drivers/nvmem/u-boot-env.c
@@ -0,0 +1,236 @@
+// 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;
+
+	/* Parent device */
+	struct mtd_info *mtd;
+	size_t offset;
+	size_t size;
+
+	/* Cells */
+	struct nvmem_cell_info *cells;
+	int ncells;
+};
+
+struct u_boot_env_image_single {
+	__le32 crc32;
+	uint8_t data[0];
+} __packed;
+
+struct u_boot_env_image_redundant {
+	__le32 crc32;
+	u8 mark;
+	uint8_t data[0];
+} __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 -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);
+	}
+
+	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->size, GFP_KERNEL);
+	if (!buf) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+
+	err = mtd_read(priv->mtd, priv->offset, priv->size, &bytes, buf);
+	if ((err && !mtd_is_bitflip(err)) || bytes != priv->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, mark);
+		data_offset = offsetof(struct u_boot_env_image_redundant, data);
+		break;
+	}
+	crc32 = le32_to_cpu(*(uint32_t *)(buf + crc32_offset));
+	crc32_data_len = priv->size - crc32_data_offset;
+	data_len = priv->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->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 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 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,
+	},
+};
+module_platform_driver(u_boot_env_driver);
+
+MODULE_AUTHOR("Rafał Miłecki");
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(of, u_boot_env_of_match_table);
-- 
2.34.1