Re: [PATCH V1] spi: Add support for Double Transfer Rate (DTR) mode

[Tudor Ambarus <tudor.ambarus@linaro.org>]

On 3/26/25 2:25 PM, Mukesh Kumar Savaliya wrote:
> Hi Mark, thanks for your comment.
> 
> On 3/26/2025 6:34 PM, Mark Brown wrote:
>> On Wed, Mar 26, 2025 at 02:09:54PM +0530, Mukesh Kumar Savaliya wrote:
>>
>>> This change introduces a new field `dtr_mode` in the `spi_transfer`
>>> structure. The `dtr_mode` field allows protocol drivers to indicate if
>>> Double Transfer Rate (DTR) mode is supported for a given transfer. When
>>> `dtr_mode` is set to true, the SPI controller will use DTR mode
>>> otherwise, it will default to single transfer mode.
>>
>>> The QSPI controller driver uses this flag and configures single or
>>> double
>>> transfer rate using the controller register.
>>
>> We should have a flag in the controller indicating if it supports this,
>> and code in the core which returns an error if a driver attempts to use
>> it when the controller doesn't support it.
> Have added below in spi.h which can be set by client and controller
> driver should be using it to decide mode.
> 
> + bool        dtr_mode;
> 
> since default it's false, should continue with SDR.
> I believe for QSPI, it supports SDR or DDR, but it's not applicable to
> standard SPI right ? So not sure in which case we should return an error ?
> 

Please check how spimem is dealing with DTR, same ideas shall be applied
for spi transfers.

Cheers,
ta