Re: [PATCH v3 12/16] pinctrl: starfive: Add pinctrl driver for StarFive SoCs

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Tue, Nov 2, 2021 at 9:08 PM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
(...)
> > On Tue, Nov 2, 2021 at 6:50 PM Emil Renner Berthing <kernel@xxxxxxxx> wrote:
>
> ...
>
> > > +static int starfive_pinconf_group_set(struct pinctrl_dev *pctldev,
> > > +                                     unsigned int gsel,
> > > +                                     unsigned long *configs,
> > > +                                     unsigned int num_configs)
> > > +{
> > > +       struct starfive_pinctrl *sfp = pinctrl_dev_get_drvdata(pctldev);
> > > +       const struct group_desc *group;
> > > +       u16 mask, value;
> > > +       int i;
> > > +
> > > +       group = pinctrl_generic_get_group(pctldev, gsel);
> > > +       if (!group)
> > > +               return -EINVAL;
> > > +
> > > +       mask = 0;
> > > +       value = 0;
> > > +       for (i = 0; i < num_configs; i++) {
> > > +               int param = pinconf_to_config_param(configs[i]);
> > > +               u32 arg = pinconf_to_config_argument(configs[i]);
> > > +
> > > +               switch (param) {
> > > +               case PIN_CONFIG_BIAS_DISABLE:
> > > +                       mask |= PAD_BIAS_MASK;
> > > +                       value = (value & ~PAD_BIAS_MASK) | PAD_BIAS_DISABLE;
> > > +                       break;
> > > +               case PIN_CONFIG_BIAS_PULL_DOWN:
> > > +                       if (arg == 0)
> > > +                               return -ENOTSUPP;
> > > +                       mask |= PAD_BIAS_MASK;
> > > +                       value = (value & ~PAD_BIAS_MASK) | PAD_BIAS_PULL_DOWN;
> > > +                       break;
> > > +               case PIN_CONFIG_BIAS_PULL_UP:
> > > +                       if (arg == 0)
> > > +                               return -ENOTSUPP;
> > > +                       mask |= PAD_BIAS_MASK;
> > > +                       value = value & ~PAD_BIAS_MASK;
> > > +                       break;
> > > +               case PIN_CONFIG_DRIVE_STRENGTH:
> > > +                       mask |= PAD_DRIVE_STRENGTH_MASK;
> > > +                       value = (value & ~PAD_DRIVE_STRENGTH_MASK) |
> > > +                               starfive_drive_strength_from_max_mA(arg);
> > > +                       break;
> > > +               case PIN_CONFIG_INPUT_ENABLE:
> > > +                       mask |= PAD_INPUT_ENABLE;
> > > +                       if (arg)
> > > +                               value |= PAD_INPUT_ENABLE;
> > > +                       else
> > > +                               value &= ~PAD_INPUT_ENABLE;
> > > +                       break;
> > > +               case PIN_CONFIG_INPUT_SCHMITT_ENABLE:
> > > +                       mask |= PAD_INPUT_SCHMITT_ENABLE;
> > > +                       if (arg)
> > > +                               value |= PAD_INPUT_SCHMITT_ENABLE;
> > > +                       else
> > > +                               value &= ~PAD_INPUT_SCHMITT_ENABLE;
> > > +                       break;
> > > +               case PIN_CONFIG_SLEW_RATE:
> > > +                       mask |= PAD_SLEW_RATE_MASK;
> > > +                       value = (value & ~PAD_SLEW_RATE_MASK) |
> > > +                               ((arg << PAD_SLEW_RATE_POS) & PAD_SLEW_RATE_MASK);
> > > +                       break;
> > > +               case PIN_CONFIG_STARFIVE_STRONG_PULL_UP:
> > > +                       if (arg) {
> > > +                               mask |= PAD_BIAS_MASK;
> > > +                               value = (value & ~PAD_BIAS_MASK) |
> > > +                                       PAD_BIAS_STRONG_PULL_UP;
> > > +                       } else {
> > > +                               mask |= PAD_BIAS_STRONG_PULL_UP;
> > > +                               value = value & ~PAD_BIAS_STRONG_PULL_UP;
> > > +                       }
> > > +                       break;
> > > +               default:
> > > +                       return -ENOTSUPP;
> > > +               }
> > > +       }
> > > +
> > > +       for (i = 0; i < group->num_pins; i++)
> > > +               starfive_padctl_rmw(sfp, group->pins[i], mask, value);
> > > +
> > > +       return 0;
> > > +}
>
> Linus any comments on this code (sorry if I missed your reply)? The
> idea behind above is to skip all settings from the same category and
> apply only the last one, e.g. if we have "bias set to X", ..., "bias
> disable", ..., "bias set to Y", the hardware will see only the last
> operation, i.e. "bias set to Y". I think it may not be the best
> approach (theoretically?) since the hardware definitely may behave
> differently on the other side in case of such series of the
> configurations (yes, I have seen some interesting implementations of
> the touchpad / touchscreen GPIOs that may be affected).

That sounds weird. I think we need to look at how other drivers
deal with this.

To me it seems more natural that
starfive_padctl_rmw(sfp, group->pins[i], mask, value);
would get called at the end of each iteration of the
for (i = 0; i < num_configs; i++) loop.

Yours,
Linus Walleij