linux-kernel - Re: [PATCH v3 4/6] spi: spi-fsl-dspi: Use non-coherent memory for DMA

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Message-ID: <228fc6f7-52c2-48a8-af7e-6f2cfa7b9168@linaro.org>
Date: Wed, 25 Jun 2025 10:00:41 +0100
From: James Clark <james.clark@...aro.org>
To: Frank Li <Frank.li@....com>
Cc: Vladimir Oltean <olteanv@...il.com>, Mark Brown <broonie@...nel.org>,
 Vladimir Oltean <vladimir.oltean@....com>, Arnd Bergmann <arnd@...db.de>,
 Larisa Grigore <larisa.grigore@....com>, Christoph Hellwig <hch@....de>,
 linux-spi@...r.kernel.org, imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/6] spi: spi-fsl-dspi: Use non-coherent memory for DMA



On 24/06/2025 5:39 pm, Frank Li wrote:
> On Tue, Jun 24, 2025 at 11:35:34AM +0100, James Clark wrote:
>> Using coherent memory here isn't functionally necessary. Because the
>> change to use non-coherent memory isn't overly complex and only a few
>> synchronization points are required, we might as well do it while fixing
>> up some other DMA issues.
>>
>> Suggested-by: Arnd Bergmann <arnd@...db.de>
>> Signed-off-by: James Clark <james.clark@...aro.org>
> 
> In https://lore.kernel.org/imx/c65c752a-5b60-4f30-8d51-9a903ddd55a6@linaro.org/
> 
> look like less performance, why need this patch.
> 
> In https://lore.kernel.org/imx/ad7e9aa7-74a3-449d-8ed9-cb270fd5c718@linaro.org/
> look like better.
> 
> Any conclusion?
> 
> Need performance gain here if it is better.
> 
> Frank
> 

Hi Frank,

The performance figures for this set are in the cover letter. It's 
either the same or faster, there is no evidence of worse performance. 
The one you linked was a bad result from not testing it in DMA mode, but 
it's corrected later in that thread.

The reason the figures aren't in this commit is because it requires this 
change and the one to increase the size of the buffer.

Thanks
James