Patch "iio: hid-sensor-trigger: Fix the race with user space powering up sensors" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

iio: hid-sensor-trigger: Fix the race with user space powering up sensors

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
iio-hid-sensor-trigger-fix-the-race-with-user-space-powering-up-sensors.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Srinivas Pandruvada <[email protected]>
Date: Sat, 12 Aug 2017 09:09:21 -0700
Subject: iio: hid-sensor-trigger: Fix the race with user space powering up sensors

From: Srinivas Pandruvada <[email protected]>

commit f1664eaacec31035450132c46ed2915fd2b2049a upstream.

It has been reported for a while that with iio-sensor-proxy service the rotation only works after one suspend/resume cycle. This required a wait in the systemd unit file to avoid race. I found a Yoga 900 where I could reproduce this.

The problem scenerio is:
- During sensor driver init, enable run time PM and also set a auto-suspend for 3 seconds.
This result in one runtime resume. But there is a check to avoid
a powerup in this sequence, but rpm is active
- User space iio-sensor-proxy tries to power up the sensor. Since rpm is active it will simply return. But sensors were not actually
powered up in the prior sequence, so actaully the sensors will not work
- After 3 seconds the auto suspend kicks

If we add a wait in systemd service file to fire iio-sensor-proxy after 3 seconds, then now everything will work as the runtime resume will actually powerup the sensor as this is a user request.

To avoid this:
- Remove the check to match user requested state, this will cause a brief powerup, but if the iio-sensor-proxy starts immediately it will
still work as the sensors are ON.
- Also move the autosuspend delay to place when user requested turn off of sensors, like after user finished raw read or buffer disable

---
 drivers/iio/common/hid-sensors/hid-sensor-trigger.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -36,8 +36,6 @@ static int _hid_sensor_power_state(struc
 	s32 poll_value = 0;
 
 	if (state) {
-		if (!atomic_read(&st->user_requested_state))
-			return 0;
 		if (sensor_hub_device_open(st->hsdev))
 			return -EIO;
 

@@ -86,6 +84,9 @@ static int _hid_sensor_power_state(struc
 				       &report_val);
 	}
 
+	pr_debug("HID_SENSOR %s set power_state %d report_state %d\n",
+		 st->pdev->name, state_val, report_val);
+
 	sensor_hub_get_feature(st->hsdev, st->power_state.report_id,
 			       st->power_state.index,
 			       sizeof(state_val), &state_val);

@@ -107,6 +108,7 @@ int hid_sensor_power_state(struct hid_se
 		ret = pm_runtime_get_sync(&st->pdev->dev);
 	else {
 		pm_runtime_mark_last_busy(&st->pdev->dev);
+		pm_runtime_use_autosuspend(&st->pdev->dev);
 		ret = pm_runtime_put_autosuspend(&st->pdev->dev);
 	}
 	if (ret < 0) {

@@ -201,8 +203,6 @@ int hid_sensor_setup_trigger(struct iio_
 	/* Default to 3 seconds, but can be changed from sysfs */
 	pm_runtime_set_autosuspend_delay(&attrb->pdev->dev,
 					 3000);
-	pm_runtime_use_autosuspend(&attrb->pdev->dev);
-
 	return ret;
 error_unreg_trigger:
 	iio_trigger_unregister(trig);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/iio-hid-sensor-trigger-fix-the-race-with-user-space-powering-up-sensors.patch