Merge branch '2022-06-09-add-support-for-nvmem-api' into next

To quote the author:
This adds support for the nvmem-cells properties cropping up in manyb
device trees. This is an easy way to load configuration, version
information, or calibration data from a non-volatile memory source. For
more information, refer to patch 6 ("misc: Add support for nvmem
cells").

For the moment I have only added some integration tests using the
ethernet addresses. This hits the main code paths (looking up nvmem
cells) but doesn't test writing. I can add a few stand-alone tests if
desired.

2 files changed, 160 insertions, 1 deletions

diff --git a/include/i2c_eeprom.h b/include/i2c_eeprom.h
index 3ad565684fe..32dcb034973 100644
--- a/include/i2c_eeprom.h
+++ b/include/i2c_eeprom.h
@@ -6,6 +6,8 @@
 #ifndef __I2C_EEPROM
 #define __I2C_EEPROM
 
+struct udevice;
+
 struct i2c_eeprom_ops {
 	int (*read)(struct udevice *dev, int offset, uint8_t *buf, int size);
 	int (*write)(struct udevice *dev, int offset, const uint8_t *buf,
@@ -20,6 +22,7 @@ struct i2c_eeprom {
 	unsigned long size;
 };
 
+#if CONFIG_IS_ENABLED(I2C_EEPROM)
 /*
  * i2c_eeprom_read() - read bytes from an I2C EEPROM chip
  *
@@ -42,7 +45,8 @@ int i2c_eeprom_read(struct udevice *dev, int offset, uint8_t *buf, int size);
  *
  * Return: 0 on success, -ve on failure
  */
-int i2c_eeprom_write(struct udevice *dev, int offset, uint8_t *buf, int size);
+int i2c_eeprom_write(struct udevice *dev, int offset, const uint8_t *buf,
+		     int size);
 
 /*
  * i2c_eeprom_size() - get size of I2C EEPROM chip
@@ -53,4 +57,25 @@ int i2c_eeprom_write(struct udevice *dev, int offset, uint8_t *buf, int size);
  */
 int i2c_eeprom_size(struct udevice *dev);
 
+#else /* !I2C_EEPROM */
+
+static inline int i2c_eeprom_read(struct udevice *dev, int offset, uint8_t *buf,
+				  int size)
+{
+	return -ENOSYS;
+}
+
+static inline int i2c_eeprom_write(struct udevice *dev, int offset,
+				   const uint8_t *buf, int size)
+{
+	return -ENOSYS;
+}
+
+static inline int i2c_eeprom_size(struct udevice *dev)
+{
+	return -ENOSYS;
+}
+
+#endif /* I2C_EEPROM */
+
 #endif
diff --git a/include/nvmem.h b/include/nvmem.h
new file mode 100644
index 00000000000..822e698bdd4
--- /dev/null
+++ b/include/nvmem.h
@@ -0,0 +1,134 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2022 Sean Anderson <[email protected]>
+ */
+
+#ifndef NVMEM_H
+#define NVMEM_H
+
+/**
+ * DOC: Design
+ *
+ * The NVMEM subsystem is a "meta-uclass" in that it abstracts over several
+ * different uclasses all with read/write APIs. One approach to implementing
+ * this could be to add a new sub-device for each nvmem-style device of
+ * UCLASS_NVMEM. This subsystem has taken the approach of using the existing
+ * access methods (i2c_eeprom_write, misc_write, etc.) directly. This has the
+ * advantage of not requiring an extra device/driver, saving on binary size and
+ * runtime memory usage. On the other hand, it is not idiomatic. Similar
+ * efforts should generally use a new uclass.
+ */
+
+/**
+ * struct nvmem_cell - One datum within non-volatile memory
+ * @nvmem: The backing storage device
+ * @offset: The offset of the cell from the start of @nvmem
+ * @size: The size of the cell, in bytes
+ */
+struct nvmem_cell {
+	struct udevice *nvmem;
+	unsigned int offset;
+	size_t size;
+};
+
+struct udevice;
+
+#if CONFIG_IS_ENABLED(NVMEM)
+
+/**
+ * nvmem_cell_read() - Read the value of an nvmem cell
+ * @cell: The nvmem cell to read
+ * @buf: The buffer to read into
+ * @size: The size of @buf
+ *
+ * Return:
+ * * 0 on success
+ * * -EINVAL if @buf is not the same size as @cell.
+ * * -ENOSYS if CONFIG_NVMEM is disabled
+ * * A negative error if there was a problem reading the underlying storage
+ */
+int nvmem_cell_read(struct nvmem_cell *cell, void *buf, size_t size);
+
+/**
+ * nvmem_cell_write() - Write a value to an nvmem cell
+ * @cell: The nvmem cell to write
+ * @buf: The buffer to write from
+ * @size: The size of @buf
+ *
+ * Return:
+ * * 0 on success
+ * * -EINVAL if @buf is not the same size as @cell
+ * * -ENOSYS if @cell is read-only, or if CONFIG_NVMEM is disabled
+ * * A negative error if there was a problem writing the underlying storage
+ */
+int nvmem_cell_write(struct nvmem_cell *cell, const void *buf, size_t size);
+
+/**
+ * nvmem_cell_get_by_index() - Get an nvmem cell from a given device and index
+ * @dev: The device that uses the nvmem cell
+ * @index: The index of the cell in nvmem-cells
+ * @cell: The cell to initialize
+ *
+ * Look up the nvmem cell referenced by the phandle at @index in nvmem-cells in
+ * @dev.
+ *
+ * Return:
+ * * 0 on success
+ * * -EINVAL if the regs property is missing, empty, or undersized
+ * * -ENODEV if the nvmem device is missing or unimplemented
+ * * -ENOSYS if CONFIG_NVMEM is disabled
+ * * A negative error if there was a problem reading nvmem-cells or getting the
+ *   device
+ */
+int nvmem_cell_get_by_index(struct udevice *dev, int index,
+			    struct nvmem_cell *cell);
+
+/**
+ * nvmem_cell_get_by_name() - Get an nvmem cell from a given device and name
+ * @dev: The device that uses the nvmem cell
+ * @name: The name of the nvmem cell
+ * @cell: The cell to initialize
+ *
+ * Look up the nvmem cell referenced by @name in the nvmem-cell-names property
+ * of @dev.
+ *
+ * Return:
+ * * 0 on success
+ * * -EINVAL if the regs property is missing, empty, or undersized
+ * * -ENODEV if the nvmem device is missing or unimplemented
+ * * -ENODATA if @name is not in nvmem-cell-names
+ * * -ENOSYS if CONFIG_NVMEM is disabled
+ * * A negative error if there was a problem reading nvmem-cell-names,
+ *   nvmem-cells, or getting the device
+ */
+int nvmem_cell_get_by_name(struct udevice *dev, const char *name,
+			   struct nvmem_cell *cell);
+
+#else /* CONFIG_NVMEM */
+
+static inline int nvmem_cell_read(struct nvmem_cell *cell, void *buf, int size)
+{
+	return -ENOSYS;
+}
+
+static inline int nvmem_cell_write(struct nvmem_cell *cell, const void *buf,
+				   int size)
+{
+	return -ENOSYS;
+}
+
+static inline int nvmem_cell_get_by_index(struct udevice *dev, int index,
+					  struct nvmem_cell *cell)
+{
+	return -ENOSYS;
+}
+
+static inline int nvmem_cell_get_by_name(struct udevice *dev, const char *name,
+					 struct nvmem_cell *cell)
+{
+	return -ENOSYS;
+}
+
+#endif /* CONFIG_NVMEM */
+
+#endif /* NVMEM_H */