linux-kernel - Re: [PATCH v5 09/12] gpio: aggregator: handle runtime registration of gpio_desc in gpiochip

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMuHMdXQm9FGt8dZ0y_916od1rep2A3QNm8iS0Pm+jr0uKPD9Q@mail.gmail.com>
Date: Fri, 9 May 2025 11:29:06 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Thomas Richard <thomas.richard@...tlin.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Kees Cook <kees@...nel.org>, Andy Shevchenko <andy@...nel.org>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com, 
	DanieleCleri@...on.eu, GaryWang@...on.com.tw, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v5 09/12] gpio: aggregator: handle runtime registration of
 gpio_desc in gpiochip_fwd

Hi Thomas,

On Tue, 6 May 2025 at 17:21, Thomas Richard <thomas.richard@...tlin.com> wrote:
> Add request() callback to check if the GPIO descriptor was well registered
> in the gpiochip_fwd before using it. This is done to handle the case where
> GPIO descriptor is added at runtime in the forwarder.
>
> If at least one GPIO descriptor was not added before the forwarder
> registration, we assume the forwarder can sleep as if a GPIO is added at
> runtime it may sleep.
>
> Signed-off-by: Thomas Richard <thomas.richard@...tlin.com>

Thanks for your patch!

> --- a/drivers/gpio/gpio-aggregator.c
> +++ b/drivers/gpio/gpio-aggregator.c

> @@ -288,6 +289,21 @@ struct gpio_chip *gpio_fwd_get_gpiochip(struct gpiochip_fwd *fwd)
>  }
>  EXPORT_SYMBOL_NS_GPL(gpio_fwd_get_gpiochip, "GPIO_FORWARDER");
>
> +/**
> + * gpio_fwd_request - Request a line of the GPIO forwarder
> + * @chip: GPIO chip in the forwarder
> + * @offset: the offset of the line to request
> + *
> + * Returns: 0 on success, or negative errno on failure.
> + */
> +int gpio_fwd_request(struct gpio_chip *chip, unsigned int offset)

This function should take a gpiochip_fwd pointer instead.

> +{
> +       struct gpiochip_fwd *fwd = gpiochip_get_data(chip);
> +
> +       return test_bit(offset, fwd->valid_mask) ? 0 : -ENODEV;
> +}

Not related to this patch, but just a random note:

     * struct gpio_chip - abstract a GPIO controller
     [...[
     * @request: optional hook for chip-specific activation, such as
     *      enabling module power and clock; may sleep; must return 0 on success
     *      or negative error number on failure
     * @free: optional hook for chip-specific deactivation, such as
     *      disabling module power and clock; may sleep

Currently all GPIOs are requested when the aggregator is created,
which means they are always powered and clocked, irrespective of a
user of the aggregator has requested them or not.
I don't see how this can be improve, except by adding suspend/resume
callbacks to gpio_chip, which could be called from the aggegator's
.free() and .request() callbacks?

> +EXPORT_SYMBOL_NS_GPL(gpio_fwd_request, "GPIO_FORWARDER");
> +
>  /**
>   * gpio_fwd_get_direction - Return the current direction of a GPIO forwarder line
>   * @chip: GPIO chip in the forwarder

> @@ -675,6 +700,18 @@ int gpio_fwd_gpio_add(struct gpiochip_fwd *fwd, struct gpio_desc *desc,
>  }
>  EXPORT_SYMBOL_NS_GPL(gpio_fwd_gpio_add, "GPIO_FORWARDER");
>
> +/**
> + * gpio_fwd_gpio_free - Remove a GPIO from the forwarder
> + * @fwd: GPIO forwarder
> + * @offset: offset of GPIO to remove
> + */
> +void gpio_fwd_gpio_free(struct gpiochip_fwd *fwd, unsigned int offset)
> +{
> +       if (test_and_clear_bit(offset, fwd->valid_mask))
> +               gpiod_put(fwd->descs[offset]);
> +}
> +EXPORT_SYMBOL_NS_GPL(gpio_fwd_gpio_free, "GPIO_FORWARDER");

So this is _not_ the inverse of gpio_fwd_request()
(it has an extra "_gpio" in the name).

Naming is indeed tricky.
I was also wondering about gpio_fwd_get(), which does not get the
forwarder, but gets a GPIO of the forwarder...

> +
>  /**
>   * gpio_fwd_register - Register a GPIO forwarder
>   * @fwd: GPIO forwarder

> --- a/include/linux/gpio/forwarder.h
> +++ b/include/linux/gpio/forwarder.h
> @@ -9,6 +9,8 @@ struct gpiochip_fwd;
>
>  struct gpio_chip *gpio_fwd_get_gpiochip(struct gpiochip_fwd *fwd);
>
> +int gpio_fwd_request(struct gpio_chip *chip, unsigned int offset);
> +
>  int gpio_fwd_get_direction(struct gpio_chip *chip, unsigned int offset);
>
>  int gpio_fwd_direction_input(struct gpio_chip *chip, unsigned int offset);
> @@ -37,6 +39,8 @@ struct gpiochip_fwd *devm_gpio_fwd_alloc(struct device *dev,
>  int gpio_fwd_gpio_add(struct gpiochip_fwd *fwd,
>                       struct gpio_desc *desc, unsigned int offset);
>
> +void gpio_fwd_gpio_free(struct gpiochip_fwd *fwd, unsigned int offset);
> +
>  int gpio_fwd_register(struct gpiochip_fwd *fwd);

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds