linux-kernel - Re: [RFT PATCH] spi: bcm2835: reduce the abuse of the GPIO API

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Message-ID: <CAMRc=Md-6i+nqDtYiUUtZExA32c0nJxhevYsiZqmd1PP8aaMng@mail.gmail.com>
Date:   Fri, 1 Sep 2023 09:40:11 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>, linux-spi@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [RFT PATCH] spi: bcm2835: reduce the abuse of the GPIO API

On Fri, Sep 1, 2023 at 1:25 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Thu, Aug 31, 2023 at 09:49:34PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > Currently the bcm2835 SPI driver uses functions meant for GPIO providers
> > exclusively to locate the GPIO chip it gets its CS pins from and request
> > the relevant pin. I don't know the background and what bug forced this.
>
> ...
>
> >       /*
> > +      * TODO: The code below is a slightly better alternative to the utter
> > +      * abuse of the GPIO API that I found here before. It creates a
> > +      * temporary lookup table, assigns it to the SPI device, gets the GPIO
> > +      * descriptor and then releases the lookup table.
> >        *
> > +      * Still the real problem is unsolved. Looks like the cs_gpiods table
> > +      * is not assigned correctly from DT?
> >        */
>
> I'm not sure why this quirk is here. AFAIR the SPI CS quirks are located in
> gpiolib-of.c.
>

I'm not sure this is a good candidate for the GPIOLIB quirks. This is
the SPI setup callback (which makes me think - I should have used
gpiod_get(), not devm_gpiod_get() and then put the descriptor in
.cleanup()) and not probe. It would be great to get some background on
why this is even needed in the first place. The only reason I see is
booting the driver with an invalid device-tree that doesn't assign the
GPIO to the SPI controller.

Bart