linux-kernel - Re: [RFT PATCH v2] spi: bcm2835: reduce the abuse of the GPIO API

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Message-ID: <CACRpkdYLcOZQ9r46aBwesh-H392C_0AWC8n2ikuwUknfEhoNNA@mail.gmail.com>
Date:   Fri, 1 Sep 2023 14:15:39 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Mark Brown <broonie@...nel.org>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        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>,
        Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [RFT PATCH v2] spi: bcm2835: reduce the abuse of the GPIO API

On Fri, Sep 1, 2023 at 1:15 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> Currently the bcm2835 SPI driver uses functions that are available
> exclusively to GPIO providers as a way to handle a platform quirk. Let's
> use a slightly better alternative that avoids poking around in GPIOLIB's
> internals and use GPIO lookup tables.
>
> Link: https://www.spinics.net/lists/linux-gpio/msg36218.html
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

> +#include <linux/cleanup.h>
(...)
> -       struct gpio_chip *chip;
> +       struct gpiod_lookup_table *lookup __free(kfree) = NULL;

Whoa!
This is really neat.
As noted, it will confuse static checkers at no end, but they just have
to adopt. (CC to Dan C if he now runs into this.)

> +       gpiod_add_lookup_table(lookup);

Maybe we should mention the obvious advantage to the previous
hack: if there is a "cs-gpios" in the device tree, it will take precedence,
because gpiod_find_and_request() will try gpiod_find_by_fwnode()
*first* and only if this fails it will fall back to gpiod_find().

Hm, maybe we should go and fix these device trees? :P

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij