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Subject: Re: [PATCH] spi: dt-bindings: clarify CS behavior for spi-cs-high and gpio descriptors
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From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <CAGngYiVL9M72hFRWnmT_8RRX9pUTSLsNuYz6mUo0Be4Vivk7Xw@mail.gmail.com>
Date:   Wed, 9 Dec 2020 20:31:55 +0100
Cc:     Mark Brown <broonie@kernel.org>, Rob Herring <robh+dt@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-spi <linux-spi@vger.kernel.org>,
        linux-gpio@vger.kernel.org,
        devicetree <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>, kernel@pyra-handheld.com,
        Lukas Wunner <lukas@wunner.de>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Andreas Kemnade <andreas@kemnade.info>,
        Maxime Ripard <maxime@cerno.tech>
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References: <3bed61807fff6268789e7d411412fbc5cd6ffe2a.1607507863.git.hns@goldelico.com> <CAGngYiVKHoXPGxmScCnb-R6xoo9GNw5pG8V8Cpyk3meoJbskiw@mail.gmail.com> <3FA1D050-3BD5-4A97-9D83-520CCF75D147@goldelico.com> <CAGngYiVL9M72hFRWnmT_8RRX9pUTSLsNuYz6mUo0Be4Vivk7Xw@mail.gmail.com>
To:     Sven Van Asbroeck <thesven73@gmail.com>
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> Am 09.12.2020 um 20:04 schrieb Sven Van Asbroeck =
<thesven73@gmail.com>:
>=20
> On Wed, Dec 9, 2020 at 1:16 PM H. Nikolaus Schaller =
<hns@goldelico.com> wrote:
>>=20
>> 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...
>=20
> The inversion you witnessed was a bug caused by spi client drivers =
that

The inversion we witnessed came from:

commit 6953c57ab172 "gpio: of: Handle SPI chipselect legacy bindings"

There, I read a verbal description of the table I want to formalize
with this patch, because natural language is not as precise as the =
language
of logic.

This has nothing to do with driver code, which remained and remains =
unchanged
for long time.

>=20
>> Secondly, please imagine some reader of a device tree who finds
>>=20
>>       cs-gpios =3D <&gpio 7 ACTIVE_LOW>;
>>       spi-cs-high;
>=20
> That reader looks at the rules, sees that:
> - the ACTIVE_LOW is ignored,
> - presence of spi-cs-high means active-high
> and concludes this chip-select is active-high.

This misses information what the reader should do to resolve the
obviously missing beauty of the DT.

a) remove spi-cs-high;
b) change to ACTIVE_HIGH

Both appear valid in first place. But one is preferred. This is
again nowhere documented if you simplify the table.