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

-----Original Message-----
From: Srinivas Kandagatla <redacted>
Sent: 2021年8月11日 17:52
To: Joakim Zhang <redacted>; robh+dt@kernel.org;
shawnguo@kernel.org
Cc: kernel@pengutronix.de; dl-linux-imx <redacted>;
devicetree@vger.kernel.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH V1 2/4] nvmem: core: introduce "reverse-data" property
to reverse buffer



On 10/08/2021 08:35, Joakim Zhang wrote:

quoted

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

Is all the data stored in imx-ocopt reverse byte order?

No, it depends on how users program these data.

or someone decided to change the order for only mac-address?

No, will not change the order for mac-address, would be consistent.

quoted

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 <redacted>
---
  drivers/nvmem/core.c           | 30

++++++++++++++++++++++++++++++

quoted

  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;

This flag also needs to go in struct nvmem_cell_info too.

OK.

quoted

  };

  static DEFINE_MUTEX(nvmem_mutex);

@@ -92,6 +93,26 @@ static int __nvmem_reg_write(struct nvmem_device

*nvmem, unsigned int offset,

quoted

  	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];
+

You could possibly simplify this.

static void nvmem_buffer_reverse(u8 *buf, int len) {
	int i;

	for (i = 0; i < len/2; i++)
		swap(buf[i], buf[len - i - 1]);
}

Thanks.

quoted

+	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)

quoted

  		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 @@

quoted

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)

Maybe NVMEM_FLAGS_REVERSE_BYTE_ORDER and some kerneldoc would
help new users.

Yes, will rename it, could you please point me where nvmem kerneldoc there to add new info?

Best Regards,
Joakim Zhang

--srini

quoted

+
  /**
   * struct nvmem_keepout - NVMEM register keepout range.
   *