Re: [PATCH v2] serial: mctrl_gpio: Support all GPIO suffixes (gpios vs gpio)

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

CC Mika, who reported the initial issue

On Thu, Aug 15, 2019 at 10:53 AM Stefan Roese <sr@xxxxxxx> wrote:
>
> This patch fixes a backward compatibility issue, when boards use the
> old style GPIO suffix "-gpio" instead of the new "-gpios". This
> potential problem has been introduced by commit d99482673f95 ("serial:
> mctrl_gpio: Check if GPIO property exisits before requesting it").
>
> This patch now fixes this issue by using gpiod_count() which iterates
> over all supported GPIO suffixes (thanks to Linus for suggesting this).
>
> With this change, the local string is not needed any more. This way
> we can remove the allocation in the loop.
>
> Signed-off-by: Stefan Roese <sr@xxxxxxx>
> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Cc: Pavel Machek <pavel@xxxxxxx>
> Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> v2
> - Use gpiod_count() to check if the GPIO exists (Linus)
> - Remove the now unnecessary malloc in the loop (kasprintf)
>
>  drivers/tty/serial/serial_mctrl_gpio.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/tty/serial/serial_mctrl_gpio.c b/drivers/tty/serial/serial_mctrl_gpio.c
> index 2b400189be91..ce73b142c66b 100644
> --- a/drivers/tty/serial/serial_mctrl_gpio.c
> +++ b/drivers/tty/serial/serial_mctrl_gpio.c
> @@ -117,18 +117,11 @@ struct mctrl_gpios *mctrl_gpio_init_noauto(struct device *dev, unsigned int idx)
>
>         for (i = 0; i < UART_GPIO_MAX; i++) {
>                 enum gpiod_flags flags;
> -               char *gpio_str;
> -               bool present;
> +               int count;
>
>                 /* Check if GPIO property exists and continue if not */
> -               gpio_str = kasprintf(GFP_KERNEL, "%s-gpios",
> -                                    mctrl_gpios_desc[i].name);
> -               if (!gpio_str)
> -                       continue;
> -
> -               present = device_property_present(dev, gpio_str);
> -               kfree(gpio_str);
> -               if (!present)
> +               count = gpiod_count(dev, mctrl_gpios_desc[i].name);
> +               if (count <= 0)
>                         continue;
>
>                 if (mctrl_gpios_desc[i].dir_out)

Seems like both device_property_present() and gpiod_count()
eventually call into acpi_data_get_property().

However, given
commit 6fe9da42f1d98fdb4be1598e230aca97e66cf35d
Author: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Date:   Tue May 23 20:03:20 2017 +0300

    gpio: acpi: Synchronize acpi_find_gpio() and acpi_gpio_count()

    If we pass connection ID to the both functions and at the same time
    acpi_can_fallback_to_crs() returns false we will get different results,
    i.e. the number of GPIO resources returned by acpi_gpio_count() might be
    not correct.

    Fix this by calling acpi_can_fallback_to_crs() in acpi_gpio_count()
    before trying to fallback.

acpi_find_gpio() and acpi_gpio_count() are supposed to use the exact
same logic, so this patch is not gonna work as intended?!?

Note that I still find it strange that acpi_find_gpio() falls back to
unnamed gpios if con_id != NULL, causing the problem in the first place.
This is gonna bite us again later...

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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