drm/amd/display: Skip Recompute DSC Params if no Stream on Link

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Skip Recompute DSC Params if no Stream on Link

[why]

Encounter NULL pointer dereference uner mst + dsc setup.

BUG: kernel NULL pointer dereference, address: 0000000000000008

PGD 0 P4D 0

Oops: 0000 [#1] PREEMPT SMP NOPTI

CPU: 4 PID: 917 Comm: sway Not tainted 6.3.9-arch1-1 #1 124dc55df4f5272ccb409f39ef4872fc2b3376a2

Hardware name: LENOVO 20NKS01Y00/20NKS01Y00, BIOS R12ET61W(1.31 ) 07/28/2022

RIP: 0010:drm_dp_atomic_find_time_slots+0x5e/0x260 [drm_display_helper]

Code: 01 00 00 48 8b 85 60 05 00 00 48 63 80 88 00 00 00 3b 43 28 0f 8d 2e 01 00 00 48 8b 53 30 48 8d 04 80 48 8d 04 c2 48 8b 40 18 <48> 8>

RSP: 0018:ffff960cc2df77d8 EFLAGS: 00010293

RAX: 0000000000000000 RBX: ffff8afb87e81280 RCX: 0000000000000224

RDX: ffff8afb9ee37c00 RSI: ffff8afb8da1a578 RDI: ffff8afb87e81280

RBP: ffff8afb83d67000 R08: 0000000000000001 R09: ffff8afb9652f850

R10: ffff960cc2df7908 R11: 0000000000000002 R12: 0000000000000000

R13: ffff8afb8d7688a0 R14: ffff8afb8da1a578 R15: 0000000000000224

FS: 00007f4dac35ce00(0000) GS:ffff8afe30b00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000000000008 CR3: 000000010ddc6000 CR4: 00000000003506e0

Call Trace:

<TASK>

? __die+0x23/0x70

? page_fault_oops+0x171/0x4e0

? plist_add+0xbe/0x100

? exc_page_fault+0x7c/0x180

? asm_exc_page_fault+0x26/0x30

? drm_dp_atomic_find_time_slots+0x5e/0x260 [drm_display_helper 0e67723696438d8e02b741593dd50d80b44c2026]

? drm_dp_atomic_find_time_slots+0x28/0x260 [drm_display_helper 0e67723696438d8e02b741593dd50d80b44c2026]

compute_mst_dsc_configs_for_link+0x2ff/0xa40 [amdgpu 62e600d2a75e9158e1cd0a243bdc8e6da040c054]

? fill_plane_buffer_attributes+0x419/0x510 [amdgpu 62e600d2a75e9158e1cd0a243bdc8e6da040c054]

compute_mst_dsc_configs_for_state+0x1e1/0x250 [amdgpu 62e600d2a75e9158e1cd0a243bdc8e6da040c054]

amdgpu_dm_atomic_check+0xecd/0x1190 [amdgpu 62e600d2a75e9158e1cd0a243bdc8e6da040c054]

drm_atomic_check_only+0x5c5/0xa40

drm_mode_atomic_ioctl+0x76e/0xbc0

[how]

dsc recompute should be skipped if no mode change detected on the new

request. If detected, keep checking whether the stream is already on

current state or not.