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Subject: Re: [PATCH v2] reset: make shared pulsed reset controls
 re-triggerable
To:     Philipp Zabel <p.zabel@pengutronix.de>
Cc:     linux-kernel@vger.kernel.org, linux-amlogic@lists.infradead.org,
        linux-usb@vger.kernel.org, Jerome Brunet <jbrunet@baylibre.com>,
        Kevin Hilman <khilman@baylibre.com>,
        Jim Quinlan <james.quinlan@broadcom.com>
References: <20201112230043.28987-1-aouledameur@baylibre.com>
From:   Amjad Ouled-Ameur <aouledameur@baylibre.com>
Message-ID: <96bce8ff-9601-e6cc-94b1-abd9583e19ae@baylibre.com>
Date:   Fri, 13 Nov 2020 01:12:48 +0100
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Please find in this patchset [0] a use case of the reset_control_rearm() call
on some of meson usb drivers:


[0] https://lore.kernel.org/lkml/20201113000508.14702-1-aouledameur@baylibre.com/

On 13/11/2020 00:00, Amjad Ouled-Ameur wrote:

> 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_rearm() 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_rearm() 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.
>
> Signed-off-by: Amjad Ouled-Ameur <aouledameur@baylibre.com>
> Reported-by: Jerome Brunet <jbrunet@baylibre.com>
> ---
> Change since v1: [0]
> * Renamed the new call from reset_control_(array_)resettable to
> reset_control_(array_)rearm
> * Open-coded reset_control_array_rearm to check for errors before
> decrementing triggered_count because we cannot roll back in case an
> error occurs while decrementing one of the rstc.
> * Reworded the new call's description.
>
> [0] https://lore.kernel.org/lkml/20201001132758.12280-1-aouledameur@baylibre.com
>
>   drivers/reset/core.c  | 73 +++++++++++++++++++++++++++++++++++++++++++
>   include/linux/reset.h |  1 +
>   2 files changed, 74 insertions(+)
>
> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> index a2df88e90011..34e89aa0fb5e 100644
> --- a/drivers/reset/core.c
> +++ b/drivers/reset/core.c
> @@ -208,6 +208,39 @@ static int reset_control_array_reset(struct reset_control_array *resets)
>   	return 0;
>   }
>   
> +static int reset_control_array_rearm(struct reset_control_array *resets)
> +{
> +	struct reset_control *rstc;
> +	int i;
> +
> +	for (i = 0; i < resets->num_rstcs; i++) {
> +		rstc = resets->rstc[i];
> +
> +		if (!rstc)
> +			continue;
> +
> +		if (WARN_ON(IS_ERR(rstc)))
> +			return -EINVAL;
> +
> +		if (rstc->shared) {
> +			if (WARN_ON(atomic_read(&rstc->deassert_count) != 0))
> +				return -EINVAL;
> +		} else {
> +			if (!rstc->acquired)
> +				return -EPERM;
> +		}
> +	}
> +
> +	for (i = 0; i < resets->num_rstcs; i++) {
> +		rstc = resets->rstc[i];
> +
> +		if (rstc && rstc->shared)
> +			WARN_ON(atomic_dec_return(&rstc->triggered_count) < 0);
> +	}
> +
> +	return 0;
> +}
> +
>   static int reset_control_array_assert(struct reset_control_array *resets)
>   {
>   	int ret, i;
> @@ -325,6 +358,46 @@ int reset_control_reset(struct reset_control *rstc)
>   }
>   EXPORT_SYMBOL_GPL(reset_control_reset);
>   
> +/**
> + * reset_control_rearm - allow shared reset line to be re-triggered"
> + * @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 call is used.
> + *
> + * Calls to this function must be balanced with calls to reset_control_reset,
> + * a warning is thrown in case triggered_count ever dips below 0.
> + *
> + * Consumers must not use reset_control_(de)assert on shared reset lines when
> + * reset_control_reset or reset_control_rearm have been used.
> + *
> + * If rstc is NULL the function will just return 0.
> + */
> +int reset_control_rearm(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_rearm(rstc_to_array(rstc));
> +
> +	if (rstc->shared) {
> +		if (WARN_ON(atomic_read(&rstc->deassert_count) != 0))
> +			return -EINVAL;
> +
> +		WARN_ON(atomic_dec_return(&rstc->triggered_count) < 0);
> +	} else {
> +		if (!rstc->acquired)
> +			return -EPERM;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(reset_control_rearm);
> +
>   /**
>    * reset_control_assert - asserts the reset line
>    * @rstc: reset controller
> diff --git a/include/linux/reset.h b/include/linux/reset.h
> index 05aa9f440f48..439fec7112a9 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_rearm(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);