[PATCH] drm/panthor: Fix a race between the reset and suspend path

[Boris Brezillon]

If a reset is scheduled when the suspend happens, we drop the
reset-pending info on the floor assuming the resume will fix things,
but the resume logic might try a fast reset. If we're lucky, the
fast reset fails and we fallback to a slow reset, but if the FW was
corrupted in a way that makes it partially functional (it boots but
doesn't quite do what it's expected to do), we won't notice immediately
that things are not working correctly, leading to a new reset further
down the road.

Fixes: 5fe909cae118 ("drm/panthor: Add the device logical block")
Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
---
 drivers/gpu/drm/panthor/panthor_device.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
index 2c817e65e6be..3285ac42d2cd 100644
--- a/drivers/gpu/drm/panthor/panthor_device.c
+++ b/drivers/gpu/drm/panthor/panthor_device.c
@@ -128,14 +128,11 @@ static void panthor_device_reset_work(struct work_struct *work)
 	struct panthor_device *ptdev = container_of(work, struct panthor_device, reset.work);
 	int ret = 0, cookie;
 
-	if (atomic_read(&ptdev->pm.state) != PANTHOR_DEVICE_PM_STATE_ACTIVE) {
-		/*
-		 * No need for a reset as the device has been (or will be)
-		 * powered down
-		 */
-		atomic_set(&ptdev->reset.pending, 0);
+	/* If the device is entering suspend, we don't reset. A slow reset will
+	 * be forced at resume time instead.
+	 */
+	if (atomic_read(&ptdev->pm.state) != PANTHOR_DEVICE_PM_STATE_ACTIVE)
 		return;
-	}
 
 	if (!drm_dev_enter(&ptdev->base, &cookie))
 		return;
@@ -473,6 +470,14 @@ int panthor_device_resume(struct device *dev)
 
 	if (panthor_device_is_initialized(ptdev) &&
 	    drm_dev_enter(&ptdev->base, &cookie)) {
+		/* If there was a reset pending at the time we suspended the
+		 * device, we force a slow reset.
+		 */
+		if (atomic_read(&ptdev->reset.pending)) {
+			ptdev->reset.fast = false;
+			atomic_set(&ptdev->reset.pending, 0);
+		}
+
 		ret = panthor_device_resume_hw_components(ptdev);
 		if (ret && ptdev->reset.fast) {
 			drm_err(&ptdev->base, "Fast reset failed, trying a slow reset");
@@ -489,9 +494,6 @@ int panthor_device_resume(struct device *dev)
 			goto err_suspend_devfreq;
 	}
 
-	if (atomic_read(&ptdev->reset.pending))
-		queue_work(ptdev->reset.wq, &ptdev->reset.work);
-
 	/* Clear all IOMEM mappings pointing to this device after we've
 	 * resumed. This way the fake mappings pointing to the dummy pages
 	 * are removed and the real iomem mapping will be restored on next
-- 
2.47.0