nvmem: core: add nvmem cell post processing callback

Some NVMEM providers have certain nvmem cells encoded, which requires
post processing before actually using it.

For example mac-address is stored in either in ascii or delimited or reverse-order.

Having a post-process callback hook to provider drivers would enable them to
do this vendor specific post processing before nvmem consumers see it.
Tested-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20211013131957.30271-3-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -38,6 +38,7 @@ struct nvmem_device {
 	unsigned int		nkeepout;
 	nvmem_reg_read_t	reg_read;
 	nvmem_reg_write_t	reg_write;
+	nvmem_cell_post_process_t cell_post_process;
 	struct gpio_desc	*wp_gpio;
 	void *priv;
 };
@@ -796,6 +797,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	nvmem->type = config->type;
 	nvmem->reg_read = config->reg_read;
 	nvmem->reg_write = config->reg_write;
+	nvmem->cell_post_process = config->cell_post_process;
 	nvmem->keepout = config->keepout;
 	nvmem->nkeepout = config->nkeepout;
 	if (config->of_node)
@@ -1440,6 +1442,13 @@ static int __nvmem_cell_read(struct nvmem_device *nvmem,
 	if (cell->bit_offset || cell->nbits)
 		nvmem_shift_read_buffer_in_place(cell, buf);
 
+	if (nvmem->cell_post_process) {
+		rc = nvmem->cell_post_process(nvmem->priv, id,
+					      cell->offset, buf, cell->bytes);
+		if (rc)
+			return rc;
+	}
+
 	if (len)
 		*len = cell->bytes;
 

include/linux/nvmem-provider.h

@@ -19,6 +19,9 @@ typedef int (*nvmem_reg_read_t)(void *priv, unsigned int offset,
 				void *val, size_t bytes);
 typedef int (*nvmem_reg_write_t)(void *priv, unsigned int offset,
 				 void *val, size_t bytes);
+/* used for vendor specific post processing of cell data */
+typedef int (*nvmem_cell_post_process_t)(void *priv, const char *id, unsigned int offset,
+					  void *buf, size_t bytes);
 
 enum nvmem_type {
 	NVMEM_TYPE_UNKNOWN = 0,
@@ -62,6 +65,7 @@ struct nvmem_keepout {
  * @no_of_node:	Device should not use the parent's of_node even if it's !NULL.
  * @reg_read:	Callback to read data.
  * @reg_write:	Callback to write data.
+ * @cell_post_process:	Callback for vendor specific post processing of cell data
  * @size:	Device size.
  * @word_size:	Minimum read/write access granularity.
  * @stride:	Minimum read/write access stride.
@@ -92,6 +96,7 @@ struct nvmem_config {
 	bool			no_of_node;
 	nvmem_reg_read_t	reg_read;
 	nvmem_reg_write_t	reg_write;
+	nvmem_cell_post_process_t cell_post_process;
 	int	size;
 	int	word_size;
 	int	stride;