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

Rafał Miłecki
2022-06-11T20:47:44Z

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);
+ }
+
+ 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