linux-kernel - Re: [PATCH 1/8] gpio: Add Elba SoC gpio driver for spi cs control

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Message-ID: <CACRpkdZEURRTe15HGf93SvyHej=_6qhfP9KWPSQbCM=SLUVKmA@mail.gmail.com>
Date:   Sun, 29 Aug 2021 23:09:19 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Brad Larson <brad@...sando.io>, Mark Brown <broonie@...nel.org>,
        Serge Semin <fancer.lancer@...il.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Olof Johansson <olof@...om.net>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/8] gpio: Add Elba SoC gpio driver for spi cs control

On Mon, Aug 23, 2021 at 3:06 AM Brad Larson <brad@...sando.io> wrote:

> The gpio pins being used for the Elba SoC SPI CS are dedicated to this
> function.  Are you recommending that the code in
> drivers/gpio/gpio-elba-spics.c be integrated into
> drivers/spi/spi-dw-mmio.c?

That makes most sense does it not?

Special purpose pins should be managed by that special purpose
hardware driver, DW SPI in this case.

The compatible string etc should be enough to determine that we
need some extra GPIO control here, possibly specify extra registers
for the SPI host etc.

The struct spi_master has a special callback .set_cs() and you
should make this behave special for your special hardware.
In the case of the DW driver it appears that even subdrivers can
pass a custom version of this call in struct dw_spi.

Yours,
Linus Walleij