Re: [PATCH V3 1/2] pinctrl: bcm2835: Implement bcm2835_pinconf_get

[Chen-Yu Tsai <wens@kernel.org>]

Hi Linus,

On Sun, Mar 3, 2024 at 10:02 PM Stefan Wahren <wahrenst@gmx.net> wrote:
>
> Even the driver already has implemented pin_dbg_show, it could
> be helpful to implement pin_conf_get for a more generic behavior.
> Contrary to the BCM2711, the BCM2835 SOC doesn't allow to read
> the bias config, so the implementation is limited to the basics.
>
> Keep ENOTSUPP here, because it's only used internally.
>
> Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
> ---
>  drivers/pinctrl/bcm/pinctrl-bcm2835.c | 37 +++++++++++++++++++++++++--
>  1 file changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pinctrl/bcm/pinctrl-bcm2835.c b/drivers/pinctrl/bcm/pinctrl-bcm2835.c
> index 1489191a213f..ed768cefe5d0 100644
> --- a/drivers/pinctrl/bcm/pinctrl-bcm2835.c
> +++ b/drivers/pinctrl/bcm/pinctrl-bcm2835.c
> @@ -1003,8 +1003,41 @@ static const struct pinmux_ops bcm2835_pmx_ops = {
>  static int bcm2835_pinconf_get(struct pinctrl_dev *pctldev,
>                         unsigned pin, unsigned long *config)
>  {
> -       /* No way to read back config in HW */
> -       return -ENOTSUPP;
> +       enum pin_config_param param = pinconf_to_config_param(*config);
> +       struct bcm2835_pinctrl *pc = pinctrl_dev_get_drvdata(pctldev);
> +       enum bcm2835_fsel fsel = bcm2835_pinctrl_fsel_get(pc, pin);
> +       u32 val;
> +
> +       /* No way to read back bias config in HW */
> +
> +       switch (param) {
> +       case PIN_CONFIG_INPUT_ENABLE:
> +               if (fsel != BCM2835_FSEL_GPIO_IN)
> +                       return -EINVAL;
> +
> +               *config = pinconf_to_config_packed(param, 1);
> +               break;
> +
> +       case PIN_CONFIG_OUTPUT_ENABLE:
> +               if (fsel != BCM2835_FSEL_GPIO_OUT)
> +                       return -EINVAL;
> +
> +               *config = pinconf_to_config_packed(param, 1);
> +               break;

I'd like to take this opportunity to ask about INPUT_ENABLE and
OUTPUT_ENABLE.

AFAICT from existing comments in include/linux/pinctrl/pinconf-generic.h ,
these two options refer to input and output buffers or connections within
the general electric path, i.e. it allows the signal to pass through in
a certain direction. It does not refer to the current selected direction
of the GPIO function, which is covered by the PIN_CONFIG_OUTPUT option,
and by gpiolib, if and only if the pin has been allocated for gpiolib
use. But it seems multiple existing drivers do this.

What's the correct thing to do here?


Thanks
ChenYu

> +
> +       case PIN_CONFIG_OUTPUT:
> +               if (fsel != BCM2835_FSEL_GPIO_OUT)
> +                       return -EINVAL;
> +
> +               val = bcm2835_gpio_get_bit(pc, GPLEV0, pin);
> +               *config = pinconf_to_config_packed(param, val);
> +               break;
> +
> +       default:
> +               return -ENOTSUPP;
> +       }
> +
> +       return 0;
>  }
>
>  static void bcm2835_pull_config_set(struct bcm2835_pinctrl *pc,
> --
> 2.34.1
>
>
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