[PATCH V1 2/4] nvmem: core: introduce "reverse-data" property to reverse buffer

[Joakim Zhang <qiangqing.zhang@xxxxxxx>]

This patch intends to introduce "reverse-data" property at nvmem
provider side to reverse buffer.

For a case used from Ethernet driver, of_get_mac_address() may call
of_get_mac_addr_nvmem() to get MAC address from nvmem device. MAC address
programed in imx-ocopt is MSB first in lowest address, so need reverse
data then feedback to nvmem consumer. E.g. MAC address read from
imx-ocopt is 98:e2:06:9f:04:00, after reversed the data is
00:04:9f:06:e2:98.

Signed-off-by: Joakim Zhang <qiangqing.zhang@xxxxxxx>
---
 drivers/nvmem/core.c           | 30 ++++++++++++++++++++++++++++++
 include/linux/nvmem-provider.h |  2 ++
 2 files changed, 32 insertions(+)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index b3bc30a04ed7..ccc2c5801c8e 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -55,6 +55,7 @@ struct nvmem_cell {
 	struct device_node	*np;
 	struct nvmem_device	*nvmem;
 	struct list_head	node;
+	u32			flags;
 };
 
 static DEFINE_MUTEX(nvmem_mutex);
@@ -92,6 +93,26 @@ static int __nvmem_reg_write(struct nvmem_device *nvmem, unsigned int offset,
 	return -EINVAL;
 }
 
+static int nvmem_buffer_reverse(void *bufaddr, int len)
+{
+	u8 *buf = (u8 *)bufaddr;
+	u8 *temp;
+	int i;
+
+	temp = kzalloc(len, GFP_KERNEL);
+	if (!temp)
+		return -ENOMEM;
+
+	memcpy(temp, buf, len);
+
+	for (i = 0; i < len; i++)
+		buf[i] = temp[len - i - 1];
+
+	kfree(temp);
+
+	return 0;
+}
+
 static int nvmem_access_with_keepouts(struct nvmem_device *nvmem,
 				      unsigned int offset, void *val,
 				      size_t bytes, int write)
@@ -705,6 +726,9 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
 		cell->bytes = be32_to_cpup(addr);
 		cell->name = kasprintf(GFP_KERNEL, "%pOFn", child);
 
+		if (of_property_read_bool(child, "reverse-data"))
+			cell->flags |= NVMEM_FLAGS_REVERSE_DATA;
+
 		addr = of_get_property(child, "bits", &len);
 		if (addr && len == (2 * sizeof(u32))) {
 			cell->bit_offset = be32_to_cpup(addr++);
@@ -1398,6 +1422,12 @@ static int __nvmem_cell_read(struct nvmem_device *nvmem,
 	if (cell->bit_offset || cell->nbits)
 		nvmem_shift_read_buffer_in_place(cell, buf);
 
+	if (cell->flags & NVMEM_FLAGS_REVERSE_DATA) {
+		rc = nvmem_buffer_reverse(buf, cell->bytes);
+		if (rc < 0)
+			return rc;
+	}
+
 	if (len)
 		*len = cell->bytes;
 
diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index 104505e9028f..364ac2a61b11 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -31,6 +31,8 @@ enum nvmem_type {
 #define NVMEM_DEVID_NONE	(-1)
 #define NVMEM_DEVID_AUTO	(-2)
 
+#define NVMEM_FLAGS_REVERSE_DATA	BIT(0)
+
 /**
  * struct nvmem_keepout - NVMEM register keepout range.
  *
-- 
2.17.1