Re: [PATCH v5] regulator: core: Resolve supply name earlier to prevent double-init

[Saravana Kannan <saravanak@google.com>]

On Thu, Aug 25, 2022 at 2:28 PM Christian Kohlschütter
<christian@kohlschutter.com> wrote:
>
> Previously, an unresolved regulator supply reference upon calling
> regulator_register on an always-on or boot-on regulator caused
> set_machine_constraints to be called twice.
>
> This in turn may initialize the regulator twice, leading to voltage
> glitches that are timing-dependent. A simple, unrelated configuration
> change may be enough to hide this problem, only to be surfaced by
> chance.

In your case, can you elaborate which part of the constraints/init
twice caused the issue?

I'm trying to simplify some of the supply resolving code and I'm
trying to not break your use case.

-Saravana

>
> One such example is the SD-Card voltage regulator in a NanoPI R4S that
> would not initialize reliably unless the registration flow was just
> complex enough to allow the regulator to properly reset between calls.
>
> Fix this by re-arranging regulator_register, trying resolve the
> regulator's supply early enough that set_machine_constraints does not
> need to be called twice.
>
> Signed-off-by: Christian Kohlschütter <christian@kohlschutter.com>
> ---
>  drivers/regulator/core.c | 58 ++++++++++++++++++++++++----------------
>  1 file changed, 35 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
> index 77f60eef960..2ff0ab2730f 100644
> --- a/drivers/regulator/core.c
> +++ b/drivers/regulator/core.c
> @@ -5391,6 +5391,7 @@ regulator_register(const struct regulator_desc *regulator_desc,
>         bool dangling_of_gpiod = false;
>         struct device *dev;
>         int ret, i;
> +       bool resolved_early = false;
>
>         if (cfg == NULL)
>                 return ERR_PTR(-EINVAL);
> @@ -5494,24 +5495,10 @@ regulator_register(const struct regulator_desc *regulator_desc,
>         BLOCKING_INIT_NOTIFIER_HEAD(&rdev->notifier);
>         INIT_DELAYED_WORK(&rdev->disable_work, regulator_disable_work);
>
> -       /* preform any regulator specific init */
> -       if (init_data && init_data->regulator_init) {
> -               ret = init_data->regulator_init(rdev->reg_data);
> -               if (ret < 0)
> -                       goto clean;
> -       }
> -
> -       if (config->ena_gpiod) {
> -               ret = regulator_ena_gpio_request(rdev, config);
> -               if (ret != 0) {
> -                       rdev_err(rdev, "Failed to request enable GPIO: %pe\n",
> -                                ERR_PTR(ret));
> -                       goto clean;
> -               }
> -               /* The regulator core took over the GPIO descriptor */
> -               dangling_cfg_gpiod = false;
> -               dangling_of_gpiod = false;
> -       }
> +       if (init_data && init_data->supply_regulator)
> +               rdev->supply_name = init_data->supply_regulator;
> +       else if (regulator_desc->supply_name)
> +               rdev->supply_name = regulator_desc->supply_name;
>
>         /* register with sysfs */
>         rdev->dev.class = &regulator_class;
> @@ -5533,13 +5520,38 @@ regulator_register(const struct regulator_desc *regulator_desc,
>                 goto wash;
>         }
>
> -       if (init_data && init_data->supply_regulator)
> -               rdev->supply_name = init_data->supply_regulator;
> -       else if (regulator_desc->supply_name)
> -               rdev->supply_name = regulator_desc->supply_name;
> +       if ((rdev->supply_name && !rdev->supply) &&
> +               (rdev->constraints->always_on ||
> +                rdev->constraints->boot_on)) {
> +               ret = regulator_resolve_supply(rdev);
> +               if (ret != 0)
> +                       rdev_dbg(rdev, "Unable to resolve supply early: %pe\n",
> +                                ERR_PTR(ret));
> +
> +               resolved_early = true;
> +       }
> +
> +       /* perform any regulator specific init */
> +       if (init_data && init_data->regulator_init) {
> +               ret = init_data->regulator_init(rdev->reg_data);
> +               if (ret < 0)
> +                       goto wash;
> +       }
> +
> +       if (config->ena_gpiod) {
> +               ret = regulator_ena_gpio_request(rdev, config);
> +               if (ret != 0) {
> +                       rdev_err(rdev, "Failed to request enable GPIO: %pe\n",
> +                                        ERR_PTR(ret));
> +                       goto wash;
> +               }
> +               /* The regulator core took over the GPIO descriptor */
> +               dangling_cfg_gpiod = false;
> +               dangling_of_gpiod = false;
> +       }
>
>         ret = set_machine_constraints(rdev);
> -       if (ret == -EPROBE_DEFER) {
> +       if (ret == -EPROBE_DEFER && !resolved_early) {
>                 /* Regulator might be in bypass mode and so needs its supply
>                  * to set the constraints
>                  */
> --
> 2.36.2
>
>