media: mediatek: vcodec: prevent kernel crash when scp ipi timeout

media: mediatek: vcodec: prevent kernel crash when scp ipi timeout

When SCP timeout during playing video, kernel crashes with following
message. It's caused by accessing NULL pointer in vpu_dec_ipi_handler.
This patch doesn't solve the root cause of NULL pointer, but merely
prevent kernel crashed when encounter the NULL pointer.

After applied this patch, kernel keeps alive, only the video player turns
to green screen.

[67242.065474] pc : vpu_dec_ipi_handler+0xa0/0xb20 [mtk_vcodec_dec]
[67242.065485] [MTK_V4L2] level=0 fops_vcodec_open(),334:
18000000.vcodec_dec decoder [135]
[67242.065523] lr : scp_ipi_handler+0x11c/0x244 [mtk_scp]
[67242.065540] sp : ffffffbb4207fb10
[67242.065557] x29: ffffffbb4207fb30 x28: ffffffd00a1d5000
[67242.065592] x27: 1ffffffa0143aa24 x26: 0000000000000000
[67242.065625] x25: dfffffd000000000 x24: ffffffd0168bfdb0
[67242.065659] x23: 1ffffff76840ff74 x22: ffffffbb41fa8a88
[67242.065692] x21: ffffffbb4207fb9c x20: ffffffbb4207fba0
[67242.065725] x19: ffffffbb4207fb98 x18: 0000000000000000
[67242.065758] x17: 0000000000000000 x16: ffffffd042022094
[67242.065791] x15: 1ffffff77ed4b71a x14: 1ffffff77ed4b719
[67242.065824] x13: 0000000000000000 x12: 0000000000000000
[67242.065857] x11: 0000000000000000 x10: dfffffd000000001
[67242.065890] x9 : 0000000000000000 x8 : 0000000000000002
[67242.065923] x7 : 0000000000000000 x6 : 000000000000003f
[67242.065956] x5 : 0000000000000040 x4 : ffffffffffffffe0
[67242.065989] x3 : ffffffd043b841b8 x2 : 0000000000000000
[67242.066021] x1 : 0000000000000010 x0 : 0000000000000010
[67242.066055] Call trace:
[67242.066092]  vpu_dec_ipi_handler+0xa0/0xb20 [mtk_vcodec_dec
12220d230d83a7426fc38c56b3e7bc6066955bae]
[67242.066119]  scp_ipi_handler+0x11c/0x244 [mtk_scp
8fb69c2ef141dd3192518b952b65aba35627b8bf]
[67242.066145]  mt8192_scp_irq_handler+0x70/0x128 [mtk_scp
8fb69c2ef141dd3192518b952b65aba35627b8bf]
[67242.066172]  scp_irq_handler+0xa0/0x114 [mtk_scp
8fb69c2ef141dd3192518b952b65aba35627b8bf]
[67242.066200]  irq_thread_fn+0x84/0xf8
[67242.066220]  irq_thread+0x170/0x1ec
[67242.066242]  kthread+0x2f8/0x3b8
[67242.066264]  ret_from_fork+0x10/0x30
[67242.066292] Code: 38f96908 35003628 91004340 d343fc08 (38f96908)

Signed-off-by: Tinghan Shen <tinghan.shen@mediatek.com>
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: Macpaul Lin <macpaul.lin@mediatek.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>