linux-kernel - Re: [PATCH 2/8] spi: spi-s3s64xx: Add S3C64XX_SPI_QUIRK_CS

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Message-ID: <20200819193816.GB38371@sirena.org.uk>
Date:   Wed, 19 Aug 2020 20:38:16 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Lukasz Stelmach <l.stelmach@...sung.com>
Cc:     Krzysztof Kozlowski <krzk@...nel.org>,
        Kukjin Kim <kgene@...nel.org>, Andi Shyti <andi@...zian.org>,
        linux-spi@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        m.szyprowski@...sung.com, b.zolnierkie@...sung.com
Subject: Re: [PATCH 2/8] spi: spi-s3s64xx: Add S3C64XX_SPI_QUIRK_CS_AUTO for
 Exynos3250

On Wed, Aug 19, 2020 at 03:01:21PM +0200, Lukasz Stelmach wrote:
> It was <2020-08-19 śro 14:39>, when Krzysztof Kozlowski wrote:

> > There is here no commit msg, no explanation.

> As I wrote in the cover letter, this and previous commits make things
> work on Exynos3250 (ARTIK5 precisely). I can't explain why. I read
> everything I could about this HW and there were no details about
> automatic CS handling other than how to turn it on and off.

What is similar about those other SoCs - could you be more specific
here, or what goes wrong if you don't set this?  The auto mode (or at
least the auto mode that was on the Exynos7) is not compatible with many
SPI devices if the controller chip select is actually in use, the quirk
was added for controllers that just don't have the manual mode.

See also:

  https://lore.kernel.org/linux-spi/CAAgF-BfGwcNzMx0meFVkJqNMTbQ4_PP1PZ3i6edOm6U3bc26_Q@mail.gmail.com/

for an explanation of the quirk.

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