vcn regression on raven1

[Tom St Denis]

Hi all,

I've noticed that on the tip of drm-next vcn playback of video is broken 
(see dmesg below).  I've bisected it to this commit

[root at raven linux]# git bisect good
701372349fd55b5396b335580e979ac4dde3dd02 is the first bad commit
commit 701372349fd55b5396b335580e979ac4dde3dd02
Author: Alex Deucher <alexander.deucher at amd.com>
Date:   Tue Mar 27 17:10:56 2018 -0500

     drm/amdgpu/gmc9: use amdgpu_ring_emit_reg_write_reg_wait in gpu tlb 
flush

     Use amdgpu_ring_emit_reg_write_reg_wait.  On engines that support it,
     it provides a write and wait in a single packet which avoids a missed
     ack if a world switch happens between the request and waiting for the
     ack.

     Reviewed-by: Huang Rui <ray.huang at amd.com>
     Reviewed-by: Christian König <christian.koenig at amd.com>
     Signed-off-by: Alex Deucher <alexander.deucher at amd.com>

:040000 040000 4e4312de03f4b34abd65f4bb12dba4c7093055ba 
ccc4abc78c0b6f24328fd998f998fa06bf0618b1 M      drivers

Which is odd because the commit before this is the vcn change and it 
works fine (playing BBB right now).

Here's the dmesg:

[ 2925.640102] BUG: unable to handle kernel NULL pointer dereference at 
0000000000000000
[ 2925.640113] IP:           (null)
[ 2925.640116] PGD 0 P4D 0
[ 2925.640122] Oops: 0010 [#1] SMP KASAN NOPTI
[ 2925.640126] Modules linked in: tun fuse amdkfd amdgpu mfd_core chash 
gpu_sched ttm ax88179_178a usbnet
[ 2925.640139] CPU: 4 PID: 3791 Comm: vcn_dec Not tainted 4.16.0-rc7+ #20
[ 2925.640142] Hardware name: System manufacturer System Product 
Name/TUF B350M-PLUS GAMING, BIOS 3803 01/22/2018
[ 2925.640146] RIP: 0010:          (null)
[ 2925.640148] RSP: 0018:ffff8801d54f7790 EFLAGS: 00010206
[ 2925.640153] RAX: 0000000000000000 RBX: ffff8801d8b38420 RCX: 
00000000007c0080
[ 2925.640156] RDX: 000000000001a6fa RSI: 000000000001a6e8 RDI: 
ffff8801d8b38420
[ 2925.640159] RBP: 000000000001a6fa R08: 0000000000000080 R09: 
ffffed003aa9eef9
[ 2925.640162] R10: 0000000009c74f08 R11: fffffbfff0f5d1e7 R12: 
ffff8801d8b3277c
[ 2925.640164] R13: ffff8801d8b3001c R14: 0000000000000005 R15: 
0000000000000000
[ 2925.640168] FS:  0000000000000000(0000) GS:ffff8801dcf00000(0000) 
knlGS:0000000000000000
[ 2925.640171] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2925.640174] CR2: 0000000000000000 CR3: 00000001d9712000 CR4: 
00000000003406e0
[ 2925.640176] Call Trace:
[ 2925.640272]  ? gmc_v9_0_emit_flush_gpu_tlb+0x260/0x2a0 [amdgpu]
[ 2925.640368]  ? vcn_v1_0_dec_ring_insert_start+0x360/0x360 [amdgpu]
[ 2925.640459]  ? mmhub_v1_0_get_clockgating+0xc0/0xc0 [amdgpu]
[ 2925.640545]  ? amdgpu_vmid_had_gpu_reset+0x89/0xc0 [amdgpu]
[ 2925.640640]  ? vcn_v1_0_dec_ring_emit_vm_flush+0x64/0xb0 [amdgpu]
[ 2925.640725]  ? amdgpu_vm_flush+0xb43/0xcc0 [amdgpu]
[ 2925.640810]  ? amdgpu_vm_need_pipeline_sync+0x260/0x260 [amdgpu]
[ 2925.640897]  ? amdgpu_vmid_had_gpu_reset+0xc0/0xc0 [amdgpu]
[ 2925.641003]  ? vcn_v1_0_dec_ring_insert_start+0x2d7/0x360 [amdgpu]
[ 2925.641095]  ? amdgpu_ib_schedule+0x1b5/0x800 [amdgpu]
[ 2925.641102]  ? dma_fence_add_callback+0x15f/0x360
[ 2925.641201]  ? amdgpu_job_run+0x32f/0x370 [amdgpu]
[ 2925.641297]  ? amdgpu_job_free_resources+0xd0/0xd0 [amdgpu]
[ 2925.641302]  ? __queue_delayed_work+0x144/0x1d0
[ 2925.641306]  ? delayed_work_timer_fn+0x40/0x40
[ 2925.641312]  ? prepare_to_wait_exclusive+0x1d0/0x1d0
[ 2925.641318]  ? drm_sched_main+0x68c/0x940 [gpu_sched]
[ 2925.641323]  ? drm_sched_entity_fini+0x60/0x60 [gpu_sched]
[ 2925.641328]  ? save_stack+0x89/0xb0
[ 2925.641332]  ? wait_woken+0x110/0x110
[ 2925.641337]  ? ret_from_fork+0x22/0x40
[ 2925.641343]  ? __schedule+0xd30/0xd30
[ 2925.641346]  ? remove_wait_queue+0x150/0x150
[ 2925.641353]  ? rcu_note_context_switch+0x2a0/0x2a0
[ 2925.641359]  ? __lock_text_start+0x8/0x8
[ 2925.641367]  ? drm_sched_entity_fini+0x60/0x60 [gpu_sched]
[ 2925.641371]  ? kthread+0x19b/0x1c0
[ 2925.641376]  ? kthread_create_worker_on_cpu+0xc0/0xc0
[ 2925.641382]  ? ret_from_fork+0x22/0x40
[ 2925.641387] Code:  Bad RIP value.
[ 2925.641397] RIP:           (null) RSP: ffff8801d54f7790
[ 2925.641400] CR2: 0000000000000000
[ 2925.641405] ---[ end trace 0684cc0468f60fb1 ]---


Note that regular compute/gfx workflows work fine on the tip of drm-next 
only vcn playback triggeers this (haven't tried encode yet...).

Cheers,
Tom