linux-kernel - Re: [PATCH 4/6] spi: spi-mem: reject partial cycle transfers in 8D-8D-8D mode

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Message-ID: <20210507153132.GC6383@sirena.org.uk>
Date:   Fri, 7 May 2021 16:31:32 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Pratyush Yadav <p.yadav@...com>
Cc:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Michael Walle <michael@...le.cc>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org
Subject: Re: [PATCH 4/6] spi: spi-mem: reject partial cycle transfers in
 8D-8D-8D mode

On Fri, May 07, 2021 at 07:26:33PM +0530, Pratyush Yadav wrote:

> Patches 2 and 3 are a slightly different matter. They add an extra 
> register write. But most controllers I've come across don't support 
> 1-byte writes in 8D mode. It is likely that they are sending 
> bogus/undefined values in the second byte and deasserting CS only after 
> the cycle is done. So they should _in theory_ change undefined behaviour 
> to defined behaviour.

> Still, they introduce an extra register write. I'm not sure how 
> risk-tolerant you want to be for stable backports. I will leave the 
> judgement to you or Tudor or Vignesh.

Ah, given that if nobody's seeing any issues I'd probably just hold off
there TBH.

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