linux-kernel - Re: [PATCH] thermal/core: Emit a warning if the thermal zone is updated without ops

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Message-ID: <2b8ce280-cb91-fb23-d19a-00dcee2a3e5a@arm.com>
Date:   Tue, 8 Dec 2020 09:36:56 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rui.zhang@...el.com, Thara Gopinath <thara.gopinath@...aro.org>,
        Amit Kucheria <amitk@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thermal/core: Emit a warning if the thermal zone is
 updated without ops

Hi Daniel,

On 12/7/20 7:05 PM, Daniel Lezcano wrote:
> The actual code is silently ignoring a thermal zone update when a
> driver is requesting it without a get_temp ops set.
> 
> That looks not correct, as the caller should not have called this
> function if the thermal zone is unable to read the temperature.
> 
> That makes the code less robust as the check won't detect the driver
> is inconsistently using the thermal API and that does not help to
> improve the framework as these circumvolutions hide the problem at the
> source.

Make sense.

> 
> In order to detect the situation when it happens, let's add a warning
> when the update is requested without the get_temp() ops set.
> 
> Any warning emitted will have to be fixed at the source of the
> problem: the caller must not call thermal_zone_device_update if there
> is not get_temp callback set.
> 
> As the check is done in thermal_zone_get_temperature() via the
> update_temperature() function, it is pointless to have the check and
> the WARN in the thermal_zone_device_update() function. Just remove the
> check and let the next call to raise the warning.
> 
> Cc: Thara Gopinath <thara.gopinath@...aro.org>
> Cc: Amit Kucheria <amitk@...nel.org>
> Cc: linux-pm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>   drivers/thermal/thermal_core.c | 16 ++++++++--------
>   1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 90e38cc199f4..1bd23ff2247b 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -448,17 +448,17 @@ static void handle_thermal_trip(struct thermal_zone_device *tz, int trip)
>   	monitor_thermal_zone(tz);
>   }
>   
> -static void update_temperature(struct thermal_zone_device *tz)
> +static int update_temperature(struct thermal_zone_device *tz)
>   {
>   	int temp, ret;
>   
>   	ret = thermal_zone_get_temp(tz, &temp);
>   	if (ret) {
>   		if (ret != -EAGAIN)
> -			dev_warn(&tz->device,
> -				 "failed to read out thermal zone (%d)\n",
> -				 ret);
> -		return;
> +			dev_warn_once(&tz->device,
> +				      "failed to read out thermal zone (%d)\n",
> +				      ret);
> +		return ret;
>   	}
>   
>   	mutex_lock(&tz->lock);
> @@ -469,6 +469,8 @@ static void update_temperature(struct thermal_zone_device *tz)
>   	trace_thermal_temperature(tz);
>   
>   	thermal_genl_sampling_temp(tz->id, temp);
> +
> +	return 0;
>   }
>   
>   static void thermal_zone_device_init(struct thermal_zone_device *tz)
> @@ -553,11 +555,9 @@ void thermal_zone_device_update(struct thermal_zone_device *tz,
>   	if (atomic_read(&in_suspend))
>   		return;
>   
> -	if (!tz->ops->get_temp)
> +	if (update_temperature(tz))
>   		return;
>   
> -	update_temperature(tz);
> -

I think the patch does a bit more. Previously we continued running the
code below even when the thermal_zone_get_temp() returned an error (due
to various reasons). Now we stop and probably would not schedule next
polling, not calling:
handle_thermal_trip() and monitor_thermal_zone()

I would left update_temperature(tz) as it was and not check the return.
The function thermal_zone_get_temp() can protect itself from missing
tz->ops->get_temp(), so we should be safe.

What do you think?

Regards,
Lukasz