Re: [PATCH] gpiolib: fix hogs with multiple lines

[Geert Uytterhoeven]

Hi Bartosz,

On Wed, 25 Mar 2026 at 11:18, Bartosz Golaszewski
<bartosz.golaszewski@xxxxxxxxxxxxxxxx> wrote:
> After moving GPIO hog handling into GPIOLIB core, we accidentally stopped
> supporting devicetree hog definitions with multiple lines like so:
>
>         hog {
>                 gpio-hog;
>                 gpios = <3 0>, <4 GPIO_ACTIVE_LOW>;
>                 output-high;
>                 line-name = "foo";
>         };
>
> Restore this functionality to fix reported regressions.
>
> Fixes: d1d564ec4992 ("gpio: move hogs into GPIO core")
> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/CAMuHMdX6RuZXAozrF5m625ZepJTVVr4pcyKczSk12MedWvoejw@xxxxxxxxxxxxxx/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>

Thanks, that fixes the issue I saw on Marzen
Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -938,12 +938,12 @@ int gpiochip_add_hog(struct gpio_chip *gc, struct fwnode_handle *fwnode)
>         struct fwnode_handle *gc_node = dev_fwnode(&gc->gpiodev->dev);
>         struct fwnode_reference_args gpiospec;
>         enum gpiod_flags dflags;
> +       const char *name = NULL;
>         struct gpio_desc *desc;
>         unsigned long lflags;
> -       const char *name;
> +       size_t num_hogs;
>         int ret, argc;
> -       u32 gpios[3]; /* We support up to three-cell bindings. */
> -       u32 cells;
> +       u32 cells = 0;

Shouldn't the default be 2?

>
>         lflags = GPIO_LOOKUP_FLAGS_DEFAULT;
>         dflags = GPIOD_ASIS;
> @@ -952,43 +952,21 @@ int gpiochip_add_hog(struct gpio_chip *gc, struct fwnode_handle *fwnode)
>         argc = fwnode_property_count_u32(fwnode, "gpios");
>         if (argc < 0)
>                 return argc;
> -       if (argc > 3)
> +
> +       ret = fwnode_property_read_u32(gc_node, "#gpio-cells", &cells);

Should this call be protected by is_of_node(), like in the old code?

> +       if ((ret && is_of_node(fwnode)) || (!ret && (argc % cells)))
>                 return -EINVAL;
>
> +       num_hogs = ret ? 1 : (argc / cells);

While you avoid modulo and division by zero due to the check for ret,
using a default would let you always validate argc against cells,
and remove the need for special casing num_hogs.

> +
> +       u32 *gpios __free(kfree) = kcalloc(argc, sizeof(u32), GFP_KERNEL);

kzalloc_objs()?

> +       if (!gpios)
> +               return -ENOMEM;
> +
>         ret = fwnode_property_read_u32_array(fwnode, "gpios", gpios, argc);
>         if (ret < 0)
>                 return ret;
>
> -       if (is_of_node(fwnode)) {
> -               /*
> -                * OF-nodes need some additional special handling for
> -                * translating of devicetree flags.
> -                */
> -               ret = fwnode_property_read_u32(gc_node, "#gpio-cells", &cells);
> -               if (ret)
> -                       return ret;
> -               if (!ret && argc != cells)
> -                       return -EINVAL;
> -
> -               memset(&gpiospec, 0, sizeof(gpiospec));
> -               gpiospec.fwnode = fwnode;
> -               gpiospec.nargs = argc;
> -
> -               for (int i = 0; i < argc; i++)
> -                       gpiospec.args[i] = gpios[i];
> -
> -               ret = of_gpiochip_get_lflags(gc, &gpiospec, &lflags);
> -               if (ret)
> -                       return ret;
> -       } else {
> -               /*
> -                * GPIO_ACTIVE_LOW is currently the only lookup flag
> -                * supported for non-OF firmware nodes.
> -                */
> -               if (gpios[1])
> -                       lflags |= GPIO_ACTIVE_LOW;
> -       }
> -
>         if (fwnode_property_present(fwnode, "input"))
>                 dflags |= GPIOD_IN;
>         else if (fwnode_property_present(fwnode, "output-low"))
> @@ -1000,11 +978,41 @@ int gpiochip_add_hog(struct gpio_chip *gc, struct fwnode_handle *fwnode)
>
>         fwnode_property_read_string(fwnode, "line-name", &name);
>
> -       desc = gpiochip_get_desc(gc, gpios[0]);
> -       if (IS_ERR(desc))
> -               return PTR_ERR(desc);
> +       for (unsigned int i = 0; i < num_hogs; i++) {
> +               if (is_of_node(fwnode)) {
> +                       /*
> +                        * OF-nodes need some additional special handling for
> +                        * translating of devicetree flags.
> +                        */
> +                       memset(&gpiospec, 0, sizeof(gpiospec));
> +                       gpiospec.fwnode = fwnode;
> +                       gpiospec.nargs = cells;
> +
> +                       for (int j = 0; j < cells; j++)
> +                               gpiospec.args[j] = gpios[i * cells + j];
> +
> +                       ret = of_gpiochip_get_lflags(gc, &gpiospec, &lflags);
> +                       if (ret)
> +                               return ret;
> +               } else {
> +                       /*
> +                        * GPIO_ACTIVE_LOW is currently the only lookup flag
> +                        * supported for non-OF firmware nodes.
> +                        */
> +                       if (gpios[i * cells + 1])

This depends on cells being non-zero, and thus having a proper default,
too.

> +                               lflags |= GPIO_ACTIVE_LOW;
> +               }
>
> -       return gpiod_hog(desc, name, lflags, dflags);
> +               desc = gpiochip_get_desc(gc, gpios[i * cells]);
> +               if (IS_ERR(desc))
> +                       return PTR_ERR(desc);
> +
> +               ret = gpiod_hog(desc, name, lflags, dflags);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return 0;
>  }
>
>  static int gpiochip_hog_lines(struct gpio_chip *gc)

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