[PATCH v3 2/3] nvmem: core: add nvmem_cell_write_variable_u32()

[Jennifer Berringer <jberring@redhat.com>]

This function allows nvmem consumers to write values of different sizes
(1-4 bytes) to an nvmem cell without knowing the exact size, akin to a
write counterpart to nvmem_cell_read_variable_le_32(). It discards the
higher order bytes of the passed u32 value based on CPU endianness as
necessary before writing to a cell smaller than 4 bytes.

Signed-off-by: Jennifer Berringer <jberring@redhat.com>
---
 drivers/nvmem/core.c           | 24 ++++++++++++++++++++++++
 include/linux/nvmem-consumer.h |  6 ++++++
 2 files changed, 30 insertions(+)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 4a5a6efe4bab..4c26a5e8c361 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1815,6 +1815,30 @@ int nvmem_cell_write(struct nvmem_cell *cell, void *buf, size_t len)
 
 EXPORT_SYMBOL_GPL(nvmem_cell_write);
 
+/**
+ * nvmem_cell_write_variable_u32() - Write up to 32-bits of data as a host-endian number
+ *
+ * @cell: nvmem cell to be written.
+ * @val: Value to be written which may be truncated.
+ *
+ * Return: length of bytes written or negative on failure.
+ */
+int nvmem_cell_write_variable_u32(struct nvmem_cell *cell, u32 val)
+{
+	struct nvmem_cell_entry *entry = cell->entry;
+	u8 *buf = (u8 *) &val;
+
+	if (!entry || entry->bytes > sizeof(u32))
+		return -EINVAL;
+
+#ifdef __BIG_ENDIAN
+	buf += sizeof(u32) - entry->bytes;
+#endif
+
+	return __nvmem_cell_entry_write(entry, buf, entry->bytes);
+}
+EXPORT_SYMBOL_GPL(nvmem_cell_write_variable_u32);
+
 static int nvmem_cell_read_common(struct device *dev, const char *cell_id,
 				  void *val, size_t count)
 {
diff --git a/include/linux/nvmem-consumer.h b/include/linux/nvmem-consumer.h
index 34c0e58dfa26..955366a07867 100644
--- a/include/linux/nvmem-consumer.h
+++ b/include/linux/nvmem-consumer.h
@@ -56,6 +56,7 @@ 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);
+int nvmem_cell_write_variable_u32(struct nvmem_cell *cell, u32 val);
 int nvmem_cell_read_u8(struct device *dev, const char *cell_id, u8 *val);
 int nvmem_cell_read_u16(struct device *dev, const char *cell_id, u16 *val);
 int nvmem_cell_read_u32(struct device *dev, const char *cell_id, u32 *val);
@@ -128,6 +129,11 @@ static inline int nvmem_cell_write(struct nvmem_cell *cell,
 	return -EOPNOTSUPP;
 }
 
+static inline int nvmem_cell_write_variable_u32(struct nvmem_cell *cell, u32 val)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int nvmem_cell_read_u8(struct device *dev,
 				     const char *cell_id, u8 *val)
 {
-- 
2.46.2