Commit 0cf321c8 authored by Daniel Lezcano's avatar Daniel Lezcano Committed by Rafael J. Wysocki
Browse files

thermal/drivers/tegra: Remove unneeded lock when setting a trip point 



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: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
Suggested-by: default avatarThierry Reding <thierry.reding@gmail.com>
Acked-by: default avatarThierry Reding <treding@nvidia.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent ec2c8aae

drivers/thermal/tegra/tegra30-tsensor.c

+14 −11
Original line number Diff line number Diff line
@@ -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;

}