The function tegra_tsensor_enable_hw_channel() takes the thermal zone
lock to prevent "a potential" race with a call to set_trips()
callback.
The driver must not play with the thermal framework core code
internals.
The tegra_tsensor_enable_hw_channel() is called by:
- the suspend / resume callbacks
- the probe function after the thermal zones are registered
The thermal zone lock taken in this function is supposed to protect
from a call to the set_trips() callback which writes in the same
register.
The potential race is when suspend / resume are called at the same
time as set_trips. This one is called only in
thermal_zone_device_update().
- At suspend time, the 'in_suspend' is set, thus the
thermal_zone_device_update() bails out immediately and set_trips is
not called during this moment.
- At resume time, the thermal zone is updated at PM_POST_SUSPEND,
thus the driver has already set the TH2 temperature.
- At probe time, we register the thermal zone and then we set the
TH2. The only scenario I can see so far is the interrupt fires, the
thermal_zone_update() is called exactly at the moment
tegra_tsensor_enable_hw_channel() a few lines after registering it.
Enable the channels before setting up the interrupt. We close the
potential race window without using the thermal zone's lock.
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Suggested-by: Thierry Reding <thierry.reding@xxxxxxxxx>
---
drivers/thermal/tegra/tegra30-tsensor.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)
diff --git a/drivers/thermal/tegra/tegra30-tsensor.c b/drivers/thermal/tegra/tegra30-tsensor.c
index 4b2ea17910cd..cb584a5735ed 100644
--- a/drivers/thermal/tegra/tegra30-tsensor.c
+++ b/drivers/thermal/tegra/tegra30-tsensor.c
@@ -359,9 +359,6 @@ static int tegra_tsensor_enable_hw_channel(const struct tegra_tsensor *ts,
tegra_tsensor_get_hw_channel_trips(tzd, &hot_trip, &crit_trip);
- /* prevent potential racing with tegra_tsensor_set_trips() */
- mutex_lock(&tzd->lock);
-
dev_info_once(ts->dev, "ch%u: PMC emergency shutdown trip set to %dC\n",
id, DIV_ROUND_CLOSEST(crit_trip, 1000));
@@ -404,8 +401,6 @@ static int tegra_tsensor_enable_hw_channel(const struct tegra_tsensor *ts,
val |= FIELD_PREP(TSENSOR_SENSOR0_CONFIG0_INTR_THERMAL_RST_EN, 1);
writel_relaxed(val, tsc->regs + TSENSOR_SENSOR0_CONFIG0);
- mutex_unlock(&tzd->lock);
-
err = thermal_zone_device_enable(tzd);
if (err) {
dev_err(ts->dev, "ch%u: failed to enable zone: %d\n", id, err);
@@ -585,6 +580,20 @@ static int tegra_tsensor_probe(struct platform_device *pdev)
return err;
}
+ /*
+ * Enable the channels before setting the interrupt so
+ * set_trips() can not be called while we are setting up the
+ * register TSENSOR_SENSOR0_CONFIG1. With this we close a
+ * potential race window where we are setting up the TH2 and
+ * the temperature hits TH1 resulting to an update of the
+ * TSENSOR_SENSOR0_CONFIG1 register in the ISR.
+ */
+ for (i = 0; i < ARRAY_SIZE(ts->ch); i++) {
+ err = tegra_tsensor_enable_hw_channel(ts, i);
+ if (err)
+ return err;
+ }
+
err = devm_request_threaded_irq(&pdev->dev, irq, NULL,
tegra_tsensor_isr, IRQF_ONESHOT,
"tegra_tsensor", ts);
@@ -592,12 +601,6 @@ static int tegra_tsensor_probe(struct platform_device *pdev)
return dev_err_probe(&pdev->dev, err,
"failed to request interrupt\n");
- for (i = 0; i < ARRAY_SIZE(ts->ch); i++) {
- err = tegra_tsensor_enable_hw_channel(ts, i);
- if (err)
- return err;
- }
-
return 0;
}
--
2.34.1
