On 1/8/21 10:53 PM, David Laight wrote:
>> On 1/7/21 8:06 PM, Jakub Kicinski wrote:
>>> On Thu, 7 Jan 2021 11:00:35 -0800 Jakub Kicinski wrote:
>>>> On Thu, 7 Jan 2021 10:48:56 +0100 Marc Kleine-Budde wrote:
>>>>> +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.
>
> 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
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
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