linux-kernel - Re: [PATCH] spi: dt-bindings: clarify CS behavior for spi-cs-high and gpio descriptors

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Date:   Wed, 9 Dec 2020 21:01:33 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     "H. Nikolaus Schaller" <hns@...delico.com>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        linux-gpio@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, kernel@...a-handheld.com,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Lukas Wunner <lukas@...ner.de>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH] spi: dt-bindings: clarify CS behavior for spi-cs-high
 and gpio descriptors

On Wed, 9 Dec 2020 14:04:26 -0500
Sven Van Asbroeck <thesven73@...il.com> wrote:

> On Wed, Dec 9, 2020 at 1:16 PM H. Nikolaus Schaller <hns@...delico.com> wrote:
> >
> > This is also what made me wonder if that is really intended because then
> > the whole discussion about the cs-gpio-flags and inversion and the fixes
> > would not have been needed. The current code and fixes are all about
> > not ignoring the flags...  
> 
> The inversion you witnessed was a bug caused by spi client drivers that
> simply "plow over" the SPI_CS_HIGH mode flag. This includes the panel driver
> you're using, see:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/panel/panel-tpo-td028ttec1.c?h=v5.10-rc6#n337
> 
ah, it would be set in spi->mode and is cleared by

spi->mode = SPI_MODE_3;


Hmm, but we have
                      spi-cpol;
                        spi-cpha;
in devicetree. Why do we need that spi->mode line at all?

Regards,
Andreas