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

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Message-ID: <1734ca66-bba7-4318-96af-8658874af907@quicinc.com>
Date: Thu, 27 Mar 2025 15:40:39 +0530
From: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
To: Tudor Ambarus <tudor.ambarus@...aro.org>, 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

Thanks Tudor !

On 3/26/2025 8:18 PM, Tudor Ambarus wrote:
> 
> 
> 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.
> 
Yes, i just got it. Have kept my proposal aligning to this. Looks 
similar to spi_mem_controller_is_capable(). Please review reply to Mark 
if that is matching expectations OR have more suggestion/corrections.
> Cheers,
> ta