Re: [PATCH V3 2/2] nvmem: add driver handling U-Boot environment variables

[Sascha Hauer <sha@pengutronix.de>]

On Sat, Jun 11, 2022 at 10:46:51PM +0200, Rafał Miłecki wrote:
> 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
> 
> Current Linux's NVMEM sysfs API allows reading whole NVMEM data block.
> It can be used by user-space tools for reading U-Boot env vars block
> without the hassle of finding its location. Parsing will still need to
> be re-done there.
> 
> Kernel-parsed NVMEM cells can be read however by Linux drivers. This may
> be uesful for Ethernet drivers for reading device MAC address which is
> often stored as U-Boot env variable.
> 
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> ---
> V3: Use of_get_mtd_device_by_node() (thanks Ahmad) & update description
> V2: Drop ARCH_BCM4908 dependency as there are plenty architectures using
>     U-Boot bootloader. Thanks Srinivas.
> 
> As noticed by Ahmad a missing NVMEM subsystem feature is user-space
> access to parsed NVMEM cells. That is something I started working on
> some time ago and I'm planning to get back to at some point, please
> check:
> [PATCH 2/2] nvmem: expose NVMEM cells in sysfs
> https://lore.kernel.org/lkml/20211220064730.28806-2-zajec5@gmail.com/
> ---
>  MAINTAINERS                |   1 +
>  drivers/nvmem/Kconfig      |  11 ++
>  drivers/nvmem/Makefile     |   2 +
>  drivers/nvmem/u-boot-env.c | 231 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 245 insertions(+)
>  create mode 100644 drivers/nvmem/u-boot-env.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 475e28365385..43b427fa76b0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -20411,6 +20411,7 @@ 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 d72d879a6d34..5f1b32b953b9 100644
> --- a/drivers/nvmem/Kconfig
> +++ b/drivers/nvmem/Kconfig
> @@ -344,4 +344,15 @@ 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 c710b64f9fe4..399f9972d45b 100644
> --- a/drivers/nvmem/Makefile
> +++ b/drivers/nvmem/Makefile
> @@ -69,3 +69,5 @@ obj-$(CONFIG_NVMEM_APPLE_EFUSES)	+= nvmem-apple-efuses.o
>  nvmem-apple-efuses-y 		:= apple-efuses.o
>  obj-$(CONFIG_MICROCHIP_OTPC)	+= nvmem-microchip-otpc.o
>  nvmem-microchip-otpc-y		:= microchip-otpc.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..92c2dd11d99f
> --- /dev/null
> +++ b/drivers/nvmem/u-boot-env.c
> @@ -0,0 +1,231 @@
> +// 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;
> +	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;
> +	}
> +
> +	priv->mtd = of_get_mtd_device_by_node(np->parent);
> +	if (IS_ERR(priv->mtd)) {
> +		dev_err(dev, "Failed to get %pOF MTD: %ld\n", np->parent, PTR_ERR(priv->mtd));
> +		return PTR_ERR(priv->mtd);
> +	}

Partitions are mtd devices themselves and the mtd layer directly
associates these devices to their OF node, so it should be possible
to do a of_get_mtd_device_by_node(np) which gets you the partition.
You can use the whole mtd device then and do not have to fiddle with
reg properties, offsets and sizes in your driver yourself.

Sascha

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