Re: [PATCH 2/2] iio: adc: ti-adc161s626: use DMA-safe memory for spi_read()

[David Lechner <dlechner@baylibre.com>]

On 3/16/26 1:31 PM, Jonathan Cameron wrote:
> On Sat, 14 Mar 2026 18:13:32 -0500
> David Lechner <dlechner@baylibre.com> wrote:
> 
>> Add a DMA-safe buffer and use it for spi_read() instead of a stack
>> memory. All SPI buffers must be DMA-safe.
>>

...

>> diff --git a/drivers/iio/adc/ti-adc161s626.c b/drivers/iio/adc/ti-adc161s626.c
>> index 1d427548e0b3..6416d6a7ada0 100644
>> --- a/drivers/iio/adc/ti-adc161s626.c
>> +++ b/drivers/iio/adc/ti-adc161s626.c
>> @@ -70,6 +70,7 @@ struct ti_adc_data {
>>  
>>  	u8 read_size;
>>  	u8 shift;
>> +	u8 buf[3] __aligned(IIO_DMA_MINALIGN);
> On this. There is new generic infrastructure for marking these.
> https://elixir.bootlin.com/linux/v7.0-rc3/source/include/linux/dma-mapping.h#L720
> https://lore.kernel.org/all/01ea88055ded4d70cac70ba557680fd5fa7d9ff5.1767601130.git.mst@redhat.com/
> 
> Would look like
> 	__dma_from_device_group_begin();
> 	u8 buf[3];
> 	__dma_from_device_group_end();
> 
> Do you think we should adopt them rather than doing our own thing?

I have mixed thoughts on this.

Pros:
* This would make it more obvious it should be at the end of the struct
  but doesn't hurt if it isn't.
Cons:
* It is more verbose.
* There doesn't seem to be __dma_to_device_group_begin(), so it isn't
  clear what we should do for tx buffers.

> Slowly though I don't want the noise of a mass conversion.
> 
> As normal, advantage of standard infrastructure is cutting down
> in subsystem specific magic.
> 
> I 'think' result is the same (though it also forces the trailing padding if anything
> comes after this and needs it).