[PATCH] media: chips-media: wave5: fix panic on decoding DECODED_IDX_FLAG_SKIP

[Mattijs Korpershoek <mkorpershoek@baylibre.com>]

The display frame region information received from the vpu also
contains the frame display index: info->index_frame_display.

This index, being a s32, can be negative when a skip option is passed.
In that case, its value is DECODED_IDX_FLAG_SKIP (-2).

When disp_idx == -2, the following exception occurs:

[ 1530.782246][ T1900] Hardware name: Texas Instruments AM62P5 SK (DT)
[ 1530.788501][ T1900] pstate: a0400005 (NzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 1530.796144][ T1900] pc : wave5_vpu_dec_get_output_info+0x300/0x308 [wave5]
[ 1530.803060][ T1900] lr : wave5_vpu_dec_get_output_info+0x80/0x308 [wave5]
[ 1530.809873][ T1900] sp : ffffffc00b85bc00
[ 1530.813872][ T1900] x29: ffffffc00b85bc00 x28: 0000000000000000 x27: 0000000000000001
[ 1530.821695][ T1900] x26: 00000000fffffffd x25: 00000000ffffffff x24: ffffff8812820000
[ 1530.829516][ T1900] x23: ffffff88199f7840 x22: ffffff8873f5e000 x21: ffffffc00b85bc58
[ 1530.837336][ T1900] x20: 0000000000000000 x19: ffffff88199f7920 x18: ffffffc00a899030
[ 1530.845156][ T1900] x17: 00000000529c6ef0 x16: 00000000529c6ef0 x15: 0000000000198487
[ 1530.852975][ T1900] x14: ffffffc009f2b650 x13: 0000000000058016 x12: 0000000005000000
[ 1530.860795][ T1900] x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
[ 1530.868615][ T1900] x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000004086
[ 1530.876434][ T1900] x5 : 0000000000000001 x4 : ffffffc001454b94 x3 : ffffffc001454d94
[ 1530.884256][ T1900] x2 : ffffffc00b8201d0 x1 : 0000000000000020 x0 : 0000000000000000
[ 1530.892087][ T1900] Call trace:
[ 1530.895225][ T1900]  wave5_vpu_dec_get_output_info+0x300/0x308 [wave5]
[ 1530.901788][ T1900]  wave5_vpu_dec_finish_decode+0x6c/0x3dc [wave5]
[ 1530.908081][ T1900]  wave5_vpu_irq_thread+0x140/0x168 [wave5]
[ 1530.913856][ T1900]  irq_thread_fn+0x44/0xa4
[ 1530.918154][ T1900]  irq_thread+0x15c/0x288
[ 1530.922330][ T1900]  kthread+0x104/0x1d4
[ 1530.926247][ T1900]  ret_from_fork+0x10/0x20
[ 1530.930520][ T1900] Code: 2a1f03ea 2a1f03eb 35ffef2c 17ffff74 (d42aa240)
[ 1530.937296][ T1900] ---[ end trace 0000000000000000 ]---
[ 1530.942596][ T1900] Kernel panic - not syncing: BRK handler: Fatal exception
[ 1530.949629][ T1900] SMP: stopping secondary CPUs
[ 1530.954244][ T1900] Kernel Offset: disabled
[ 1530.958415][ T1900] CPU features: 0x00,00000000,00800184,0000421b
[ 1530.964496][ T1900] Memory Limit: none

Move the disp_info assignment after testing that the index is positive
to avoid the exception.

Fixes: 45d1a2b93277 ("media: chips-media: wave5: Add vpuapi layer")
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
---
 drivers/media/platform/chips-media/wave5/wave5-vpuapi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/platform/chips-media/wave5/wave5-vpuapi.c b/drivers/media/platform/chips-media/wave5/wave5-vpuapi.c
index 86b3993722db..1a3efb638dde 100644
--- a/drivers/media/platform/chips-media/wave5/wave5-vpuapi.c
+++ b/drivers/media/platform/chips-media/wave5/wave5-vpuapi.c
@@ -508,8 +508,8 @@ int wave5_vpu_dec_get_output_info(struct vpu_instance *inst, struct dec_output_i
 	info->rc_decoded = rect_info;
 
 	disp_idx = info->index_frame_display;
-	disp_info = &p_dec_info->dec_out_info[disp_idx];
 	if (info->index_frame_display >= 0 && info->index_frame_display < WAVE5_MAX_FBS) {
+		disp_info = &p_dec_info->dec_out_info[disp_idx];
 		if (info->index_frame_display != info->index_frame_decoded) {
 			/*
 			 * when index_frame_decoded < 0, and index_frame_display >= 0

---
base-commit: a00b3f296eac3d43328615c3113e1a74143fc67a
change-id: 20231129-wave5-panic-82ea2d30042f

Best regards,
-- 
Mattijs Korpershoek <mkorpershoek@baylibre.com>