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

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Message-ID: <c89603b7-b70c-4b55-ac87-f84ce5be2c6c@quicinc.com>
Date: Wed, 26 Mar 2025 19:55:05 +0530
From: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
To: Mark Brown <broonie@...nel.org>
CC: <linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <andersson@...nel.org>, <konradybcio@...nel.org>
Subject: Re: [PATCH V1] spi: Add support for Double Transfer Rate (DTR) mode

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 ?