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

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Date:   Mon,  7 Dec 2020 20:05:30 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     daniel.lezcano@...aro.org, rui.zhang@...el.com
Cc:     Thara Gopinath <thara.gopinath@...aro.org>,
        Amit Kucheria <amitk@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] thermal/core: Emit a warning if the thermal zone is updated without ops

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.

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);
-
 	thermal_zone_set_trips(tz);

 	tz->notify_event = event;
-- 
2.17.1