Subject: Re: [PATCH] pinctrl: sunxi: Implement function_is_gpio

From: Paul Kocialkowski <[email-masked]>
Date: Wed, 27 May 2026 10:08:38 +0200

Hi Andrew,

On Mon 25 May 26, 23:38, Andre Przywara wrote:
> On Sun, 17 May 2026 19:14:05 +0200
> Paul Kocialkowski <[email-masked]> wrote:
> 
> Hi Paul,
> 
> > The function_is_gpio pinmux op allows the core to find out whether a
> > GPIO can be safely requested from a pinctrl property and requested as a
> > GPIO at the same time.
> > 
> > This is especially useful to request a GPIO with a particular drive
> > strength, which would otherwise not be possible.
> 
> That looks a easy enough solution, but:
> 
> > Signed-off-by: Paul Kocialkowski <[email-masked]>
> > ---
> >  drivers/pinctrl/sunxi/pinctrl-sunxi.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/drivers/pinctrl/sunxi/pinctrl-sunxi.c b/drivers/pinctrl/sunxi/pinctrl-sunxi.c
> > index d3042e0c9712..6162f2d86723 100644
> > --- a/drivers/pinctrl/sunxi/pinctrl-sunxi.c
> > +++ b/drivers/pinctrl/sunxi/pinctrl-sunxi.c
> > @@ -821,6 +821,17 @@ static int sunxi_pmx_get_func_groups(struct pinctrl_dev *pctldev,
> >  	return 0;
> >  }
> >  
> > +static bool sunxi_pmx_function_is_gpio(struct pinctrl_dev *pctldev,
> > +				       unsigned function)
> > +{
> > +	struct sunxi_pinctrl *pctl = pinctrl_dev_get_drvdata(pctldev);
> > +
> > +	if (!strncmp(pctl->functions[function].name, "gpio", 4))
> 
> I wonder if this condition is a bit too relaxed? There could be
> some (theoretical) function just starting with gpio, but not being mux
> 0 or 1.

Yes maybe this is a bit too relaxed.

> So should we check for gpio_in or gpio_out, explicitly? Or at
> least use (strcmp(name, "gpio_", 5)? Or maybe even better for the mux
> value directly? Is "function" an indicator of this, or does this rely
> on the two GPIO functions being always listed first, at least so far?

I considered mathcing the function to the mux index, but we can't really rely
on Allwinner keeping GPIO to mux 0/1 either so I think the string comparison
is still the best approach.

But I am totally fine with having an explicit check against
"gpio_in" || "gpio_out".

And to answer your question it's not safe to use the function as mux value,
even though the values are the same in practice. The muxval field of
struct sunxi_desc_function should be used instead and that can be looked up by
sunxi_pinctrl_desc_find_function_by_name.

All the best,

Paul

> And what about the IRQ function? Isn't that some GPIO as well, or does
> that not count for the purpose of the function_is_gpio() callback?
> 
> Cheers,
> Andre
> 
> > +		return true;
> > +
> > +	return false;
> > +}
> > +
> >  static void sunxi_pmx_set(struct pinctrl_dev *pctldev,
> >  				 unsigned pin,
> >  				 u8 config)
> > @@ -952,6 +963,7 @@ static const struct pinmux_ops sunxi_pmx_ops = {
> >  	.get_functions_count	= sunxi_pmx_get_funcs_cnt,
> >  	.get_function_name	= sunxi_pmx_get_func_name,
> >  	.get_function_groups	= sunxi_pmx_get_func_groups,
> > +	.function_is_gpio	= sunxi_pmx_function_is_gpio,
> >  	.set_mux		= sunxi_pmx_set_mux,
> >  	.gpio_set_direction	= sunxi_pmx_gpio_set_direction,
> >  	.request		= sunxi_pmx_request,
> 

-- 
Paul Kocialkowski,

Independent contractor - sys-base - https://www.sys-base.io/
Free software developer - https://www.paulk.fr/

Expert in multimedia, graphics and embedded hardware support with Linux.