drm/panthor: Fix race with suspend during unplug

There is a race between panthor_device_unplug() and
panthor_device_suspend() which can lead to IRQ handlers running on a
powered down GPU. This is how it can happen:
- unplug routine calls drm_dev_unplug()
- panthor_device_suspend() can now execute, and will skip a lot of
  important work because the device is currently marked as unplugged.
- IRQs will remain active in this case and IRQ handlers can therefore
  try to access a powered down GPU.

The fix is simply to take the PM ref in panthor_device_unplug() a
little bit earlier, before drm_dev_unplug().

Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
Fixes: 5fe909cae118a ("drm/panthor: Add the device logical block")
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patch.msgid.link/20251022103242.1083311-1-ketil.johnsen@arm.com
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
index f3ae93153b6e8e3685b4e86da8ecf0d19cc6732a..83adacaa5760d6c9c5e7be09dcab0d0c92f1f019 100644 (file)
--- a/drivers/gpu/drm/panthor/panthor_device.c
+++ b/drivers/gpu/drm/panthor/panthor_device.c
@@ -84,6 +84,8 @@ void panthor_device_unplug(struct panthor_device *ptdev)
                return;
        }
 
+       drm_WARN_ON(&ptdev->base, pm_runtime_get_sync(ptdev->base.dev) < 0);
+
        /* Call drm_dev_unplug() so any access to HW blocks happening after
         * that point get rejected.
         */
@@ -94,8 +96,6 @@ void panthor_device_unplug(struct panthor_device *ptdev)
         */
        mutex_unlock(&ptdev->unplug.lock);
 
-       drm_WARN_ON(&ptdev->base, pm_runtime_get_sync(ptdev->base.dev) < 0);
-
        /* Now, try to cleanly shutdown the GPU before the device resources
         * get reclaimed.
         */