Re: [PATCH v4 1/6] gpio: Access `gpio_bus_type` in gpiochip_setup_dev()

[Bartosz Golaszewski]

On Wed, 11 Mar 2026 12:44:31 +0100, Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> said:
> Hi Tzung-Bi,
>
> On Mon, 23 Feb 2026 at 07:17, Tzung-Bi Shih <tzungbi@xxxxxxxxxx> wrote:
>> To make the intent clear, access `gpio_bus_type` only when it's ready in
>> gpiochip_setup_dev().
>>
>> Reviewed-by: Linus Walleij <linusw@xxxxxxxxxx>
>> Signed-off-by: Tzung-Bi Shih <tzungbi@xxxxxxxxxx>
>
> Thanks for your patch, which is now commit cc11f4ef666fbca0 ("gpio:
> Access `gpio_bus_type` in gpiochip_setup_dev()") in gpio/gpio/for-next.
>
>> --- a/drivers/gpio/gpiolib.c
>> +++ b/drivers/gpio/gpiolib.c
>> @@ -901,6 +901,8 @@ static int gpiochip_setup_dev(struct gpio_device *gdev)
>>         struct fwnode_handle *fwnode = dev_fwnode(&gdev->dev);
>>         int ret;
>>
>> +       gdev->dev.bus = &gpio_bus_type;
>> +
>>         /*
>>          * If fwnode doesn't belong to another device, it's safe to clear its
>>          * initialized flag.
>> @@ -1082,7 +1084,6 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
>>          * then make sure they get free():ed there.
>>          */
>>         gdev->dev.type = &gpio_dev_type;
>> -       gdev->dev.bus = &gpio_bus_type;
>>         gdev->dev.parent = gc->parent;
>>         device_set_node(&gdev->dev, gpiochip_choose_fwnode(gc));
>>
>
> Postponing this assignment does have an impact on early
> messages. E.g. on RBTX4927:
>
>     -gpio gpiochip0: Static allocation of GPIO base is deprecated, use
> dynamic allocation.
>     + gpiochip0: Static allocation of GPIO base is deprecated, use
> dynamic allocation.
>
> Or with CONFIG_DEBUG_GPIO=y, e.g. on BeagleBone black:
>
>     -gpio gpiochip0: (gpio-0-31): created GPIO range 0->7 ==>
> 44e10800.pinmux PIN 0->7
>     -gpio gpiochip0: (gpio-0-31): created GPIO range 8->11 ==>
> 44e10800.pinmux PIN 90->93
>     -gpio gpiochip0: (gpio-0-31): created GPIO range 12->27 ==>
> 44e10800.pinmux PIN 12->27
>     -gpio gpiochip0: (gpio-0-31): created GPIO range 28->31 ==>
> 44e10800.pinmux PIN 30->33
>     + gpiochip0: (gpio-0-31): created GPIO range 0->7 ==>
> 44e10800.pinmux PIN 0->7
>     + gpiochip0: (gpio-0-31): created GPIO range 8->11 ==>
> 44e10800.pinmux PIN 90->93
>     + gpiochip0: (gpio-0-31): created GPIO range 12->27 ==>
> 44e10800.pinmux PIN 12->27
>     + gpiochip0: (gpio-0-31): created GPIO range 28->31 ==>
> 44e10800.pinmux PIN 30->33
>      [...]
>
> Note the spaces at the beginning of the printed lines.
> Reverting the commit re-adds the "gpio" prefix.
>

As per the comment in gpiochip_add_data_with_key(): we may end up with
a functional chip before gpiochip_setup_dev() is called and so before we
assign the bus type.

dev_printk() helpers only read the name field of the bus type so it should
be safe, I don't see anyone else accessing it before we register it.

I think it makes sense to revert this commit. Tzung-Bi: what do you think?

Bart