On 1/8/21 10:53 PM, David Laight wrote:

quoted

On 1/7/21 8:06 PM, Jakub Kicinski wrote:

quoted

On Thu, 7 Jan 2021 11:00:35 -0800 Jakub Kicinski wrote:

quoted

On Thu,  7 Jan 2021 10:48:56 +0100 Marc Kleine-Budde wrote:

quoted

+struct __packed tcan4x5x_map_buf {
+	struct tcan4x5x_buf_cmd cmd;
+	u8 data[256 * sizeof(u32)];
+} ____cacheline_aligned;

Interesting attribute combo, I must say.

Looking at the rest of the patch I don't really see a reason for
__packed.  Perhaps it can be dropped?

It's the stream of bytes send via SPI to the chip. Here are both structs for
reference:

quoted

+struct __packed tcan4x5x_buf_cmd {
+	u8 cmd;
+	__be16 addr;
+	u8 len;
+};

This has to be packed, as I assume the compiler would add some space after the
"u8 cmd" to align the __be16 naturally.

Why not generate a series of 32bit words to be sent over the SPI bus.
Slightly less faffing in the code.
Then have a #define (or inline function) to merge the cmd+addr+len
into a single 32bit word.

The driver uses regmap. With proper configuration regmap already formats the
"cmd" and the "addr" in correct byte order into the first 3 bytes of the "reg_buf".

As regmap doesn't support generating a length parameter, I use the above struct
tcan4x5x_buf_cmd to set the length.

Also if the length is in 32bit units, then the data[] field
ought to be u32[].

In the regmap callback the data is passed with a void pointer and a length (in
bytes), so copying this to a "u8 data[]" felt more natural to me.

regards,
Marc

-- 
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