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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aFwQCL0tQh9peb7x@lizhi-Precision-Tower-5810>
Date: Wed, 25 Jun 2025 11:04:40 -0400
From: Frank Li <Frank.li@....com>
To: James Clark <james.clark@...aro.org>
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 Wed, Jun 25, 2025 at 10:00:41AM +0100, James Clark wrote:
>
>
> 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.

Okay! you need mention why need this change, why non-coherent better than
coherent at your case.

You descript what you already done, but not descript why need it.

for example:

"fixing up some other DMA issues", what issues exactly?

some benefit, like memcpy from/to non-coherent is faster then from/to
coherenct memory ...

of put test data here will be appreciated.

The cover letter will be lost after patch merge. When someone run git log
after some year later, they need know why need this change , what purpose ...

Frank


>
> 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
>