linux-kernel - Re: [PATCH v1 1/1] gpiolib: Read "gpio-line-names" from a firmware node

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Date:   Mon, 15 Mar 2021 10:01:47 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Marek Vasut <marex@...x.de>,
        Roman Guskov <rguskov@...electronics.com>
Subject: Re: [PATCH v1 1/1] gpiolib: Read "gpio-line-names" from a firmware node

On Fri, Mar 5, 2021 at 1:03 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On STM32MP1, the GPIO banks are subnodes of pin-controller@...02000,
> see arch/arm/boot/dts/stm32mp151.dtsi. The driver for
> pin-controller@...02000 is in drivers/pinctrl/stm32/pinctrl-stm32.c
> and iterates over all of its DT subnodes when registering each GPIO
> bank gpiochip. Each gpiochip has:
>
>   - gpio_chip.parent = dev,
>     where dev is the device node of the pin controller
>   - gpio_chip.of_node = np,
>     which is the OF node of the GPIO bank
>
> Therefore, dev_fwnode(chip->parent) != of_fwnode_handle(chip.of_node),
> i.e. pin-controller@...02000 != pin-controller@...02000/gpio@...0*000.
>
> The original code behaved correctly, as it extracted the "gpio-line-names"
> from of_fwnode_handle(chip.of_node) = pin-controller@...02000/gpio@...0*000.
>
> To achieve the same behaviour, read property from the firmware node.
>
> Fixes: 7cba1a4d5e162 ("gpiolib: generalize devprop_gpiochip_set_names() for device properties")
> Reported-by: Marek Vasut <marex@...x.de>
> Reported-by: Roman Guskov <rguskov@...electronics.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/gpio/gpiolib.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 3bc25a9c4cd6..ba88011cc79d 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -367,22 +367,18 @@ static int gpiochip_set_desc_names(struct gpio_chip *gc)
>   *
>   * Looks for device property "gpio-line-names" and if it exists assigns
>   * GPIO line names for the chip. The memory allocated for the assigned
> - * names belong to the underlying software node and should not be released
> + * names belong to the underlying firmware node and should not be released
>   * by the caller.
>   */
>  static int devprop_gpiochip_set_names(struct gpio_chip *chip)
>  {
>         struct gpio_device *gdev = chip->gpiodev;
> -       struct device *dev = chip->parent;
> +       struct fwnode_handle *fwnode = dev_fwnode(&gdev->dev);
>         const char **names;
>         int ret, i;
>         int count;
>
> -       /* GPIO chip may not have a parent device whose properties we inspect. */
> -       if (!dev)
> -               return 0;
> -
> -       count = device_property_string_array_count(dev, "gpio-line-names");
> +       count = fwnode_property_string_array_count(fwnode, "gpio-line-names");
>         if (count < 0)
>                 return 0;
>
> @@ -396,7 +392,7 @@ static int devprop_gpiochip_set_names(struct gpio_chip *chip)
>         if (!names)
>                 return -ENOMEM;
>
> -       ret = device_property_read_string_array(dev, "gpio-line-names",
> +       ret = fwnode_property_read_string_array(fwnode, "gpio-line-names",
>                                                 names, count);
>         if (ret < 0) {
>                 dev_warn(&gdev->dev, "failed to read GPIO line names\n");
> --
> 2.30.1
>

Hi Andy!

Unfortunately while this may fix the particular use-case on STM32, it
breaks all other users as the 'gpio-line-names' property doesn't live
on dev_fwnode(&gdev->dev) but on dev_fwnode(chip->parent).

How about we first look for this property on the latter and only if
it's not present descend down to the former fwnode?

Bart