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

[Mukesh Kumar Savaliya]

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 ?