linux-kernel - Re: [PATCH] reset: Add reset controller API

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Message-ID: <CAHNvnFO=kH25CqrAcndVO4xTQ2pGDFi5ZHEALpFaZaGL=e_c0Q@mail.gmail.com>
Date:   Thu, 1 Oct 2020 15:55:11 +0200
From:   Amjad Ouled-Ameur <aouledameur@...libre.com>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     linux-kernel@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-usb@...r.kernel.org, Jerome Brunet <jbrunet@...libre.com>
Subject: Re: [PATCH] reset: Add reset controller API

An update on the patch title, since we don't add an API but extend it,
The title should rather be: Add a new call to the reset framework

Le jeu. 1 oct. 2020 à 15:28, Amjad Ouled-Ameur
<aouledameur@...libre.com> a écrit :
>
> The current reset framework API does not allow to release what is done by
> reset_control_reset(), IOW decrement triggered_count. Add the new
> reset_control_resettable() call to do so.
>
> When reset_control_reset() has been called once, the counter
> triggered_count, in the reset framework, is incremented i.e the resource
> under the reset is in-use and the reset should not be done again.
> reset_control_resettable() would be the way to state that the resource is
> no longer used and, that from the caller's perspective, the reset can be
> fired again if necessary.
>
> This patch will fix a usb suspend warning seen on the libretech-cc
> related to the shared reset line. This warning was addressed by the
> previously reverted commit 7a410953d1fb ("usb: dwc3: meson-g12a: fix shared
> reset control use")
>
> Signed-off-by: Amjad Ouled-Ameur <aouledameur@...libre.com>
> Reported-by: Jerome Brunet <jbrunet@...libre.com>
> ---
>  drivers/reset/core.c  | 57 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/reset.h |  1 +
>  2 files changed, 58 insertions(+)
>
> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> index 01c0c7aa835c..53653d4b55c4 100644
> --- a/drivers/reset/core.c
> +++ b/drivers/reset/core.c
> @@ -207,6 +207,19 @@ static int reset_control_array_reset(struct reset_control_array *resets)
>         return 0;
>  }
>
> +static int reset_control_array_resettable(struct reset_control_array *resets)
> +{
> +       int ret, i;
> +
> +       for (i = 0; i < resets->num_rstcs; i++) {
> +               ret = reset_control_resettable(resets->rstc[i]);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return 0;
> +}
> +
>  static int reset_control_array_assert(struct reset_control_array *resets)
>  {
>         int ret, i;
> @@ -324,6 +337,50 @@ int reset_control_reset(struct reset_control *rstc)
>  }
>  EXPORT_SYMBOL_GPL(reset_control_reset);
>
> +/**
> + * reset_control_resettable - decrements triggered_count of the controlled device
> + * @rstc: reset controller
> + *
> + * On a shared reset line the actual reset pulse is only triggered once for the
> + * lifetime of the reset_control instance, except if this function is used.
> + * In fact, It decrements triggered_count that makes sure of not allowing
> + * a reset if triggered_count is not null.
> + *
> + * This is a no-op in case triggered_count is already null i.e shared reset line
> + * is ready to be triggered.
> + *
> + * Consumers must not use reset_control_(de)assert on shared reset lines when
> + * reset_control_reset has been used.
> + *
> + * If rstc is NULL it is an optional clear and the function will just
> + * return 0.
> + */
> +int reset_control_resettable(struct reset_control *rstc)
> +{
> +       if (!rstc)
> +               return 0;
> +
> +       if (WARN_ON(IS_ERR(rstc)))
> +               return -EINVAL;
> +
> +       if (reset_control_is_array(rstc))
> +               return reset_control_array_resettable(rstc_to_array(rstc));
> +
> +       if (rstc->shared) {
> +               if (WARN_ON(atomic_read(&rstc->deassert_count) != 0))
> +                       return -EINVAL;
> +
> +               if (atomic_read(&rstc->triggered_count) > 0)
> +                       atomic_dec(&rstc->triggered_count);
> +       } else {
> +               if (!rstc->acquired)
> +                       return -EPERM;
> +       }
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(reset_control_resettable);
> +
>  /**
>   * reset_control_assert - asserts the reset line
>   * @rstc: reset controller
> diff --git a/include/linux/reset.h b/include/linux/reset.h
> index 05aa9f440f48..ffa447d0d1d6 100644
> --- a/include/linux/reset.h
> +++ b/include/linux/reset.h
> @@ -13,6 +13,7 @@ struct reset_control;
>  #ifdef CONFIG_RESET_CONTROLLER
>
>  int reset_control_reset(struct reset_control *rstc);
> +int reset_control_resettable(struct reset_control *rstc);
>  int reset_control_assert(struct reset_control *rstc);
>  int reset_control_deassert(struct reset_control *rstc);
>  int reset_control_status(struct reset_control *rstc);
> --
> 2.17.1
>


-- 
Amjad Ouled-Ameur
Embedded Linux Engineer - Villeneuve Loubet, FR
Engit@...Libre - At the Heart of Embedded Linux