nvmem: core: add an index parameter to the cell

Sometimes a cell can represend multiple values. For example, a base
ethernet address stored in the NVMEM can be expanded into multiple
discreet ones by adding an offset.

For this use case, introduce an index parameter which is then used to
distiguish between values. This parameter will then be passed to the
post process hook which can then use it to create different values
during reading.

At the moment, there is only support for the device tree path. You can
add the index to the phandle, e.g.

  &net {
          nvmem-cells = <&base_mac_address 2>;
          nvmem-cell-names = "mac-address";
  };

  &nvmem_provider {
          base_mac_address: base-mac-address@0 {
                  #nvmem-cell-cells = <1>;
                  reg = <0 6>;
          };
  };
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230206134356.839737-13-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -60,6 +60,7 @@ struct nvmem_cell_entry {
 struct nvmem_cell {
 	struct nvmem_cell_entry *entry;
 	const char		*id;
+	int			index;
 };
 
 static DEFINE_MUTEX(nvmem_mutex);
@@ -1122,7 +1123,8 @@ struct nvmem_device *devm_nvmem_device_get(struct device *dev, const char *id)
 }
 EXPORT_SYMBOL_GPL(devm_nvmem_device_get);
 
-static struct nvmem_cell *nvmem_create_cell(struct nvmem_cell_entry *entry, const char *id)
+static struct nvmem_cell *nvmem_create_cell(struct nvmem_cell_entry *entry,
+					    const char *id, int index)
 {
 	struct nvmem_cell *cell;
 	const char *name = NULL;
@@ -1141,6 +1143,7 @@ static struct nvmem_cell *nvmem_create_cell(struct nvmem_cell_entry *entry, cons
 
 	cell->id = name;
 	cell->entry = entry;
+	cell->index = index;
 
 	return cell;
 }
@@ -1179,7 +1182,7 @@ nvmem_cell_get_from_lookup(struct device *dev, const char *con_id)
 				__nvmem_device_put(nvmem);
 				cell = ERR_PTR(-ENOENT);
 			} else {
-				cell = nvmem_create_cell(cell_entry, con_id);
+				cell = nvmem_create_cell(cell_entry, con_id, 0);
 				if (IS_ERR(cell))
 					__nvmem_device_put(nvmem);
 			}
@@ -1227,15 +1230,27 @@ struct nvmem_cell *of_nvmem_cell_get(struct device_node *np, const char *id)
 	struct nvmem_device *nvmem;
 	struct nvmem_cell_entry *cell_entry;
 	struct nvmem_cell *cell;
+	struct of_phandle_args cell_spec;
 	int index = 0;
+	int cell_index = 0;
+	int ret;
 
 	/* if cell name exists, find index to the name */
 	if (id)
 		index = of_property_match_string(np, "nvmem-cell-names", id);
 
-	cell_np = of_parse_phandle(np, "nvmem-cells", index);
-	if (!cell_np)
-		return ERR_PTR(-ENOENT);
+	ret = of_parse_phandle_with_optional_args(np, "nvmem-cells",
+						  "#nvmem-cell-cells",
+						  index, &cell_spec);
+	if (ret)
+		return ERR_PTR(ret);
+
+	if (cell_spec.args_count > 1)
+		return ERR_PTR(-EINVAL);
+
+	cell_np = cell_spec.np;
+	if (cell_spec.args_count)
+		cell_index = cell_spec.args[0];
 
 	nvmem_np = of_get_parent(cell_np);
 	if (!nvmem_np) {
@@ -1257,7 +1272,7 @@ struct nvmem_cell *of_nvmem_cell_get(struct device_node *np, const char *id)
 		return ERR_PTR(-ENOENT);
 	}
 
-	cell = nvmem_create_cell(cell_entry, id);
+	cell = nvmem_create_cell(cell_entry, id, cell_index);
 	if (IS_ERR(cell))
 		__nvmem_device_put(nvmem);
 
@@ -1410,8 +1425,8 @@ 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)
+			     struct nvmem_cell_entry *cell,
+			     void *buf, size_t *len, const char *id, int index)
 {
 	int rc;
 
@@ -1425,7 +1440,7 @@ static int __nvmem_cell_read(struct nvmem_device *nvmem,
 		nvmem_shift_read_buffer_in_place(cell, buf);
 
 	if (nvmem->cell_post_process) {
-		rc = nvmem->cell_post_process(nvmem->priv, id,
+		rc = nvmem->cell_post_process(nvmem->priv, id, index,
 					      cell->offset, buf, cell->bytes);
 		if (rc)
 			return rc;
@@ -1460,7 +1475,7 @@ void *nvmem_cell_read(struct nvmem_cell *cell, size_t *len)
 	if (!buf)
 		return ERR_PTR(-ENOMEM);
 
-	rc = __nvmem_cell_read(nvmem, cell->entry, buf, len, cell->id);
+	rc = __nvmem_cell_read(nvmem, cell->entry, buf, len, cell->id, cell->index);
 	if (rc) {
 		kfree(buf);
 		return ERR_PTR(rc);
@@ -1773,7 +1788,7 @@ ssize_t nvmem_device_cell_read(struct nvmem_device *nvmem,
 	if (rc)
 		return rc;
 
-	rc = __nvmem_cell_read(nvmem, &cell, buf, &len, NULL);
+	rc = __nvmem_cell_read(nvmem, &cell, buf, &len, NULL, 0);
 	if (rc)
 		return rc;
 

drivers/nvmem/imx-ocotp.c

@@ -222,8 +222,8 @@ static int imx_ocotp_read(void *context, unsigned int offset,
 	return ret;
 }
 
-static int imx_ocotp_cell_pp(void *context, const char *id, unsigned int offset,
-			     void *data, size_t bytes)
+static int imx_ocotp_cell_pp(void *context, const char *id, int index,
+			     unsigned int offset, void *data, size_t bytes)
 {
 	struct ocotp_priv *priv = context;
 

include/linux/nvmem-provider.h

@@ -20,8 +20,8 @@ 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, 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,