nvmem: core: allow .read_post_process() callbacks to adjust buffer

Sometimes reading NVMEM cell value involves some data reformatting. it
may require resizing available buffer. Support that.

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).

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

drivers/nvmem/core.c

@@ -1538,29 +1538,26 @@ static void nvmem_shift_read_buffer_in_place(struct nvmem_cell_entry *cell, void
 
 static int __nvmem_cell_read(struct nvmem_device *nvmem,
 			     struct nvmem_cell_entry *cell,
-			     void *buf, size_t *len, const char *id, int index)
+			     void **buf, size_t *len, const char *id, int index)
 {
 	int rc;
 
-	rc = nvmem_reg_read(nvmem, cell->offset, buf, cell->bytes);
+	rc = nvmem_reg_read(nvmem, cell->offset, *buf, *len);
 
 	if (rc)
 		return rc;
 
 	/* shift bits in-place */
 	if (cell->bit_offset || cell->nbits)
-		nvmem_shift_read_buffer_in_place(cell, buf);
+		nvmem_shift_read_buffer_in_place(cell, *buf);
 
 	if (cell->read_post_process) {
 		rc = cell->read_post_process(cell->priv, id, index,
-					     cell->offset, buf, cell->bytes);
+					     cell->offset, buf, len);
 		if (rc)
 			return rc;
 	}
 
-	if (len)
-		*len = cell->bytes;
-
 	return 0;
 }
 
@@ -1577,22 +1574,26 @@ 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;
-	u8 *buf;
+	size_t bytes = cell->entry->bytes;
+	void *buf;
 	int rc;
 
 	if (!nvmem)
 		return ERR_PTR(-EINVAL);
 
-	buf = kzalloc(cell->entry->bytes, GFP_KERNEL);
+	buf = kzalloc(bytes, GFP_KERNEL);
 	if (!buf)
 		return ERR_PTR(-ENOMEM);
 
-	rc = __nvmem_cell_read(nvmem, cell->entry, buf, len, cell->id, cell->index);
+	rc = __nvmem_cell_read(nvmem, cell->entry, &buf, &bytes, cell->id, cell->index);
 	if (rc) {
 		kfree(buf);
 		return ERR_PTR(rc);
 	}
 
+	if (len)
+		*len = bytes;
+
 	return buf;
 }
 EXPORT_SYMBOL_GPL(nvmem_cell_read);
@@ -1904,11 +1905,15 @@ ssize_t nvmem_device_cell_read(struct nvmem_device *nvmem,
 	if (!nvmem)
 		return -EINVAL;
 
+	/* Cells with read_post_process hook may realloc buffer we can't allow here */
+	if (info->read_post_process)
+		return -EINVAL;
+
 	rc = nvmem_cell_info_to_nvmem_cell_entry_nodup(nvmem, info, &cell);
 	if (rc)
 		return rc;
 
-	rc = __nvmem_cell_read(nvmem, &cell, buf, &len, NULL, 0);
+	rc = __nvmem_cell_read(nvmem, &cell, &buf, &cell.bytes, NULL, 0);
 	if (rc)
 		return rc;
 

drivers/nvmem/imx-ocotp.c

@@ -223,15 +223,15 @@ static int imx_ocotp_read(void *context, unsigned int offset,
 }
 
 static int imx_ocotp_cell_pp(void *context, const char *id, int index,
-			     unsigned int offset, void *data, size_t bytes)
+			     unsigned int offset, void **data, size_t *bytes)
 {
-	u8 *buf = data;
+	u8 *buf = *data;
 	int i;
 
 	/* Deal with some post processing of nvmem cell data */
 	if (id && !strcmp(id, "mac-address"))
-		for (i = 0; i < bytes / 2; i++)
-			swap(buf[i], buf[bytes - i - 1]);
+		for (i = 0; i < *bytes / 2; i++)
+			swap(buf[i], buf[*bytes - i - 1]);
 
 	return 0;
 }

drivers/nvmem/layouts/onie-tlv.c

@@ -75,10 +75,9 @@ static const char *onie_tlv_cell_name(u8 type)
 }
 
 static int onie_tlv_mac_read_cb(void *priv, const char *id, int index,
-				unsigned int offset, void *buf,
-				size_t bytes)
+				unsigned int offset, void **buf, size_t *bytes)
 {
-	eth_addr_add(buf, index);
+	eth_addr_add(*buf, index);
 
 	return 0;
 }

drivers/nvmem/layouts/sl28vpd.c

@@ -22,19 +22,19 @@ struct sl28vpd_v1 {
 } __packed;
 
 static int sl28vpd_mac_address_pp(void *priv, const char *id, int index,
-				  unsigned int offset, void *buf,
-				  size_t bytes)
+				  unsigned int offset, void **buf,
+				  size_t *bytes)
 {
-	if (bytes != ETH_ALEN)
+	if (*bytes != ETH_ALEN)
 		return -EINVAL;
 
 	if (index < 0)
 		return -EINVAL;
 
-	if (!is_valid_ether_addr(buf))
+	if (!is_valid_ether_addr(*buf))
 		return -EINVAL;
 
-	eth_addr_add(buf, index);
+	eth_addr_add(*buf, index);
 
 	return 0;
 }

include/linux/nvmem-provider.h

@@ -19,9 +19,8 @@ typedef int (*nvmem_reg_read_t)(void *priv, unsigned int offset,
 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, int index,
-					 unsigned int offset, void *buf,
-					 size_t bytes);
+typedef int (*nvmem_cell_post_process_t)(void *priv, const char *id, int index, unsigned int offset,
+					 void **buf, size_t *bytes);
 
 enum nvmem_type {
 	NVMEM_TYPE_UNKNOWN = 0,