[PATCH v2] nvmem: layouts: u-boot-env: add optional "env-size" property

[Jascha Sundaresan <flizarthanon@gmail.com>]

Some devices reserve a larger NVMEM region for the U-Boot environment
than the actual environment data length used by U-Boot itself. The CRC32
in the U-Boot header is calculated over the smaller data length, causing
CRC validation to fail when Linux reads the full partition.

Allow an optional device tree property "env-size" to specify the
environment data size to use for CRC computation.

v2: add missing $ref line to DT binding

Signed-off-by: Jascha Sundaresan <flizarthanon@gmail.com>
---
Changes in v2:
 - Added missing "$ref" line to schema for env-size
 - Confirmed dt_binding_check passes

 .../devicetree/bindings/nvmem/layouts/u-boot,env.yaml      | 7 +++++++
 drivers/nvmem/layouts/u-boot-env.c                         | 4 +++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml b/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
index 56a8f55d4a09..e9e75c38bd11 100644
--- a/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
+++ b/Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml
@@ -46,6 +46,12 @@ properties:
     type: object
     description: Command to use for automatic booting
 
+  env-size:
+    description:
+      Size in bytes of the environment data used by U-Boot for CRC
+      calculation. If omitted, the full NVMEM region size is used.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
   ethaddr:
     type: object
     description: Ethernet interfaces base MAC address.
@@ -104,6 +110,7 @@ examples:
 
             partition-u-boot-env {
                 compatible = "brcm,env";
+                env-size = <0x20000>;
 
                 ethaddr {
                 };
diff --git a/drivers/nvmem/layouts/u-boot-env.c b/drivers/nvmem/layouts/u-boot-env.c
index a27eeb08146f..ab32bf1291af 100644
--- a/drivers/nvmem/layouts/u-boot-env.c
+++ b/drivers/nvmem/layouts/u-boot-env.c
@@ -99,10 +99,12 @@ int u_boot_env_parse(struct device *dev, struct nvmem_device *nvmem,
 	uint32_t crc32;
 	uint32_t calc;
 	uint8_t *buf;
+	u32 env_size;
 	int bytes;
 	int err;
 
-	dev_size = nvmem_dev_size(nvmem);
+	dev_size = device_property_read_u32(dev, "env-size", &env_size) ?
+		nvmem_dev_size(nvmem) : (size_t)env_size;
 
 	buf = kzalloc(dev_size, GFP_KERNEL);
 	if (!buf) {
-- 
2.39.5