[PATCH v2 3/3] media: wave5: Fix device cleanup order to prevent kernel panic

[Xulin Sun <xulin.sun@windriver.com>]

Move video device unregistration to the beginning of the remove function
to ensure all video operations are stopped before cleaning up the worker
thread and disabling PM runtime. This prevents hardware register access
after the device has been powered down.

In polling mode, the hrtimer periodically triggers
wave5_vpu_timer_callback() which queues work to the kthread worker.
The worker executes wave5_vpu_irq_work_fn() which reads hardware
registers via wave5_vdi_read_register().

The original cleanup order disabled PM runtime and powered down hardware
before unregistering video devices. When autosuspend triggers and powers
off the hardware, the video devices are still registered and the worker
thread can still be triggered by the hrtimer, causing it to attempt
reading registers from powered-off hardware. This results in a bus error
(synchronous external abort) and kernel panic.

This causes random kernel panics during encoding operations:

  Internal error: synchronous external abort: 0000000096000010
    [#1] PREEMPT SMP
  Modules linked in: wave5 rpmsg_ctrl rpmsg_char ...
  CPU: 0 UID: 0 PID: 1520 Comm: vpu_irq_thread
    Tainted: G   M    W
  pc : wave5_vdi_read_register+0x10/0x38 [wave5]
  lr : wave5_vpu_irq_work_fn+0x28/0x60 [wave5]
  Call trace:
   wave5_vdi_read_register+0x10/0x38 [wave5]
   kthread_worker_fn+0xd8/0x238
   kthread+0x104/0x120
   ret_from_fork+0x10/0x20
  Code: aa1e03e9 d503201f f9416800 8b214000 (b9400000)
  ---[ end trace 0000000000000000 ]---
  Kernel panic - not syncing: synchronous external abort:
    Fatal exception

Fixes: 9707a6254a8a ("media: chips-media: wave5: Add the v4l2 layer")
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
---
 drivers/media/platform/chips-media/wave5/wave5-vpu.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/chips-media/wave5/wave5-vpu.c b/drivers/media/platform/chips-media/wave5/wave5-vpu.c
index 0bcd48df49d0..77d6c934d0b9 100644
--- a/drivers/media/platform/chips-media/wave5/wave5-vpu.c
+++ b/drivers/media/platform/chips-media/wave5/wave5-vpu.c
@@ -351,6 +351,10 @@ static void wave5_vpu_remove(struct platform_device *pdev)
 {
 	struct vpu_device *dev = dev_get_drvdata(&pdev->dev);
 
+	wave5_vpu_enc_unregister_device(dev);
+	wave5_vpu_dec_unregister_device(dev);
+	v4l2_device_unregister(&dev->v4l2_dev);
+
 	if (dev->irq < 0) {
 		hrtimer_cancel(&dev->hrtimer);
 		kthread_cancel_work_sync(&dev->work);
@@ -364,9 +368,6 @@ static void wave5_vpu_remove(struct platform_device *pdev)
 	mutex_destroy(&dev->hw_lock);
 	reset_control_assert(dev->resets);
 	clk_bulk_disable_unprepare(dev->num_clks, dev->clks);
-	wave5_vpu_enc_unregister_device(dev);
-	wave5_vpu_dec_unregister_device(dev);
-	v4l2_device_unregister(&dev->v4l2_dev);
 	wave5_vdi_release(&pdev->dev);
 	ida_destroy(&dev->inst_ida);
 }
-- 
2.49.1