Re: [net-next 15/19] can: tcan4x5x: rework SPI access
From: Marc Kleine-Budde <mkl@pengutronix.de>
Date: 2021-01-07 21:18:25
Also in:
linux-can
On 1/7/21 8:06 PM, Jakub Kicinski wrote:
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:
+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.
+struct __packed tcan4x5x_map_buf {
+ struct tcan4x5x_buf_cmd cmd;
+ u8 data[256 * sizeof(u32)];
+} ____cacheline_aligned; Due to the packing of the struct tcan4x5x_buf_cmd it should have a length of 4 bytes. Without __packed, will the "u8 data" come directly after the cmd? Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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