nvmem: core: support specifying both: cell raw data & post read lengths

Callback .read_post_process() is designed to modify raw cell content
before providing it to the consumer. So far we were dealing with
modifications that didn't affect cell size (length). In some cases
however cell content needs to be reformatted and resized.

It's required e.g. to provide properly formatted MAC address in case
it's stored in a non-binary format (e.g. using ASCII).

There were few discussions how to optimally handle that. Following
possible solutions were considered:
1. Allow .read_post_process() to realloc (resize) content buffer
2. Allow .read_post_process() to adjust (decrease) just buffer length
3. Register NVMEM cells using post-read sizes

The preferred solution was the last one. The problem is that simply
adjusting "bytes" in NVMEM providers would result in core code NOT
passing whole raw data to .read_post_process() callbacks. It means
callback functions couldn't do their job without somehow manually
reading original cell content on their own.

This patch deals with that by registering NVMEM cells with both lengths:
raw content one and post read one. It allows:
1. Core code to read whole raw cell content
2. Callbacks to return content they want

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230404172148.82422-35-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 212c5ba5789ffbda8f3668a04db2f3b220eb8026..a62973d010ff7b03ebbdd868b5f19851b3093c52 100644 (file)
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -50,6 +50,7 @@ struct nvmem_device {
 struct nvmem_cell_entry {
        const char              *name;
        int                     offset;
+       size_t                  raw_len;
        int                     bytes;
        int                     bit_offset;
        int                     nbits;
@@ -469,6 +470,7 @@ static int nvmem_cell_info_to_nvmem_cell_entry_nodup(struct nvmem_device *nvmem,
 {
        cell->nvmem = nvmem;
        cell->offset = info->offset;
+       cell->raw_len = info->raw_len ?: info->bytes;
        cell->bytes = info->bytes;
        cell->name = info->name;
        cell->read_post_process = info->read_post_process;
@@ -1560,7 +1562,7 @@ static int __nvmem_cell_read(struct nvmem_device *nvmem,
 {
        int rc;
 
-       rc = nvmem_reg_read(nvmem, cell->offset, buf, cell->bytes);
+       rc = nvmem_reg_read(nvmem, cell->offset, buf, cell->raw_len);
 
        if (rc)
                return rc;
@@ -1571,7 +1573,7 @@ static int __nvmem_cell_read(struct nvmem_device *nvmem,
 
        if (cell->read_post_process) {
                rc = cell->read_post_process(cell->priv, id, index,
-                                            cell->offset, buf, cell->bytes);
+                                            cell->offset, buf, cell->raw_len);
                if (rc)
                        return rc;
        }
@@ -1594,14 +1596,15 @@ static int __nvmem_cell_read(struct nvmem_device *nvmem,
  */
 void *nvmem_cell_read(struct nvmem_cell *cell, size_t *len)
 {
-       struct nvmem_device *nvmem = cell->entry->nvmem;
+       struct nvmem_cell_entry *entry = cell->entry;
+       struct nvmem_device *nvmem = entry->nvmem;
        u8 *buf;
        int rc;
 
        if (!nvmem)
                return ERR_PTR(-EINVAL);
 
-       buf = kzalloc(cell->entry->bytes, GFP_KERNEL);
+       buf = kzalloc(max_t(size_t, entry->raw_len, entry->bytes), GFP_KERNEL);
        if (!buf)
                return ERR_PTR(-ENOMEM);
 

diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index 0cf9f9490514cae39d853e07cc2e5e75243ae900..8ffb42ba0f62318ba0521c2d899accf0579d7a6b 100644 (file)
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -51,6 +51,7 @@ struct nvmem_keepout {
  * struct nvmem_cell_info - NVMEM cell description
  * @name:      Name.
  * @offset:    Offset within the NVMEM device.
+ * @raw_len:   Length of raw data (without post processing).
  * @bytes:     Length of the cell.
  * @bit_offset:        Bit offset if cell is smaller than a byte.
  * @nbits:     Number of bits.
@@ -62,6 +63,7 @@ struct nvmem_keepout {
 struct nvmem_cell_info {
        const char              *name;
        unsigned int            offset;
+       size_t                  raw_len;
        unsigned int            bytes;
        unsigned int            bit_offset;
        unsigned int            nbits;