Re: [PATCH v9 2/8] PM / devfreq: Fix devfreq_notifier_call returning errno

From: Matthias Kaehlcke <mka@chromium.org>
To: Leonard Crestez <leonard.crestez@nxp.com>
Cc: "Artur Świgoń" <a.swigon@partner.samsung.com>,
	"Abel Vesa" <abel.vesa@nxp.com>,
	"Saravana Kannan" <saravanak@google.com>,
	linux-pm@vger.kernel.org,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"NXP Linux Team" <linux-imx@nxp.com>,
	"Krzysztof Kozlowski" <krzk@kernel.org>,
	"Lukasz Luba" <l.luba@partner.samsung.com>,
	"Chanwoo Choi" <cw00.choi@samsung.com>,
	"Kyungmin Park" <kyungmin.park@samsung.com>,
	"MyungJoo Ham" <myungjoo.ham@samsung.com>,
	"Alexandre Bailon" <abailon@baylibre.com>,
	"Georgi Djakov" <georgi.djakov@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	"Jacky Bai" <ping.bai@nxp.com>
Subject: Re: [PATCH v9 2/8] PM / devfreq: Fix devfreq_notifier_call returning errno
Date: Wed, 2 Oct 2019 14:24:37 -0700	[thread overview]
Message-ID: <20191002212437.GF87296@google.com> (raw)
In-Reply-To: <10b1e5f93e7594852aa5cbfe1309bf486f70ecbb.1570044052.git.leonard.crestez@nxp.com>

On Wed, Oct 02, 2019 at 10:25:05PM +0300, Leonard Crestez wrote:
> Notifier callbacks shouldn't return negative errno but one of the
> NOTIFY_OK/DONE/BAD values.
> 
> The OPP core will ignore return values from notifiers but returning a
> value that matches NOTIFY_STOP_MASK will stop the notification chain.
> 
> Fix by always returning NOTIFY_OK.
> 
> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
> ---
>  drivers/devfreq/devfreq.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 7dc899da1172..32bbf6e80380 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -548,30 +548,32 @@ EXPORT_SYMBOL(devfreq_interval_update);
>   */
>  static int devfreq_notifier_call(struct notifier_block *nb, unsigned long type,
>  				 void *devp)
>  {
>  	struct devfreq *devfreq = container_of(nb, struct devfreq, nb);
> -	int ret;
> +	int err = -EINVAL;
>  
>  	mutex_lock(&devfreq->lock);
>  
>  	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
> -	if (!devfreq->scaling_min_freq) {
> -		mutex_unlock(&devfreq->lock);
> -		return -EINVAL;
> -	}
> +	if (!devfreq->scaling_min_freq)
> +		goto out;
>  
>  	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
> -	if (!devfreq->scaling_max_freq) {
> -		mutex_unlock(&devfreq->lock);
> -		return -EINVAL;
> -	}
> +	if (!devfreq->scaling_max_freq)
> +		goto out;
> +
> +	err = update_devfreq(devfreq);
>  
> -	ret = update_devfreq(devfreq);
> +out:
>  	mutex_unlock(&devfreq->lock);
> +	if (err)
> +		dev_err(devfreq->dev.parent,
> +			"failed to update frequency from OPP notifier (%d)\n",
> +			err);

In case an OPP freq can't be found the log doesn't provide clues
about what the problem could be. I couldn't find a clearly superior
errno value though, so I guess this is as good as it gets, unless
you want to have a dedicated message for those errors. Should be a
rare exception anyway, and previously there was no log at all.

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>

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