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

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Date:   Fri, 1 Sep 2023 11:55:48 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>, Lukas Wunner <lukas@...ner.de>
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 01, 2023 at 09:40:11AM +0200, Bartosz Golaszewski wrote:
> 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.

Maybe Lukas knows more?

-- 
With Best Regards,
Andy Shevchenko