Re: [PATCH v4 6/8] iio: adc: ad4030: Add SPI offload support

[David Lechner <dlechner@baylibre.com>]

On 10/10/25 6:19 AM, Nuno Sá wrote:
> On Wed, 2025-10-08 at 10:51 -0300, Marcelo Schmitt wrote:
>> AD4030 and similar ADCs can capture data at sample rates up to 2 mega
>> samples per second (MSPS). Not all SPI controllers are able to achieve such
>> high throughputs and even when the controller is fast enough to run
>> transfers at the required speed, it may be costly to the CPU to handle
>> transfer data at such high sample rates. Add SPI offload support for AD4030
>> and similar ADCs to enable data capture at maximum sample rates.
>>
>> Co-developed-by: Trevor Gamblin <tgamblin@baylibre.com>
>> Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
>> Co-developed-by: Axel Haslam <ahaslam@baylibre.com>
>> Signed-off-by: Axel Haslam <ahaslam@baylibre.com>
>> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
>> ---
>> Change log v3 -> v4
>> - Applied code adjustments suggested to SPI offload patch.
>> - Only select SPI_OFFLOAD_TRIGGER_PWM if (SPI_OFFLOAD && PWM).
>>
>>  drivers/iio/adc/Kconfig  |   3 +
>>  drivers/iio/adc/ad4030.c | 504 +++++++++++++++++++++++++++++++++++----
>>  2 files changed, 465 insertions(+), 42 deletions(-)
>>
>> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
>> index 58a14e6833f6..1ed091b6731a 100644
>> --- a/drivers/iio/adc/Kconfig
>> +++ b/drivers/iio/adc/Kconfig
>> @@ -62,7 +62,10 @@ config AD4030
>>  	depends on GPIOLIB
>>  	select REGMAP
>>  	select IIO_BUFFER
>> +	select IIO_BUFFER_DMA
>> +	select IIO_BUFFER_DMAENGINE
>>  	select IIO_TRIGGERED_BUFFER
>> +	select SPI_OFFLOAD_TRIGGER_PWM if (SPI_OFFLOAD && PWM)
> 
> Two things as I mentioned in [1]:
> 
> 1) Wouldn't 'imply SPI_OFFLOAD_TRIGGER_PWM' accomplish the same?
> 2) Don't we also need stubs for spi/offload/consumer.h?

It doesn't hurt to enable SPI offload support even if no controller
supports it, so I would prefer that drivers that use it just select
SPI_OFFLOAD.

> 
> [1]: https://lore.kernel.org/linux-pwm/2e82eaf275b5c8df768c8b842167c3562991e50c.camel@gmail.com/T/#t
> - Nuno Sá
>