nvmem: Add a simple NVMEM framework for consumers

This patch adds just consumers part of the framework just to enable easy
review.

Up until now, nvmem drivers were stored in drivers/misc, where they all
had to duplicate pretty much the same code to register a sysfs file,
allow in-kernel users to access the content of the devices they were
driving, etc.

This was also a problem as far as other in-kernel users were involved,
since the solutions used were pretty much different from on driver to
another, there was a rather big abstraction leak.

This introduction of this framework aims at solving this. It also
introduces DT representation for consumer devices to go get the data they
require (MAC Addresses, SoC/Revision ID, part numbers, and so on) from
the nvmems.

Having regmap interface to this framework would give much better
abstraction for nvmems on different buses.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
[Maxime Ripard: intial version of the framework]
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/nvmem-consumer.h

@@ -12,6 +12,11 @@
 #ifndef _LINUX_NVMEM_CONSUMER_H
 #define _LINUX_NVMEM_CONSUMER_H
 
+struct device;
+struct device_node;
+/* consumer cookie */
+struct nvmem_cell;
+
 struct nvmem_cell_info {
 	const char		*name;
 	unsigned int		offset;
@@ -20,4 +25,60 @@ struct nvmem_cell_info {
 	unsigned int		nbits;
 };
 
+#if IS_ENABLED(CONFIG_NVMEM)
+
+/* Cell based interface */
+struct nvmem_cell *nvmem_cell_get(struct device *dev, const char *name);
+struct nvmem_cell *devm_nvmem_cell_get(struct device *dev, const char *name);
+void nvmem_cell_put(struct nvmem_cell *cell);
+void devm_nvmem_cell_put(struct device *dev, struct nvmem_cell *cell);
+void *nvmem_cell_read(struct nvmem_cell *cell, size_t *len);
+int nvmem_cell_write(struct nvmem_cell *cell, void *buf, size_t len);
+
+#else
+
+static inline struct nvmem_cell *nvmem_cell_get(struct device *dev,
+						const char *name)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline struct nvmem_cell *devm_nvmem_cell_get(struct device *dev,
+				       const char *name)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline void devm_nvmem_cell_put(struct device *dev,
+				       struct nvmem_cell *cell)
+{
+
+}
+static inline void nvmem_cell_put(struct nvmem_cell *cell)
+{
+}
+
+static inline char *nvmem_cell_read(struct nvmem_cell *cell, size_t *len)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline int nvmem_cell_write(struct nvmem_cell *cell,
+				    const char *buf, size_t len)
+{
+	return -ENOSYS;
+}
+#endif /* CONFIG_NVMEM */
+
+#if IS_ENABLED(CONFIG_NVMEM) && IS_ENABLED(CONFIG_OF)
+struct nvmem_cell *of_nvmem_cell_get(struct device_node *np,
+				     const char *name);
+#else
+static inline struct nvmem_cell *of_nvmem_cell_get(struct device_node *np,
+				     const char *name)
+{
+	return ERR_PTR(-ENOSYS);
+}
+#endif /* CONFIG_NVMEM && CONFIG_OF */
+
 #endif  /* ifndef _LINUX_NVMEM_CONSUMER_H */