Comment 0 for bug 1814308

[impact]

The amdgpu driver, when configured with MST monitors (i.e. displayport "daisy-chaining"), encounters a WARNING when blanking - such as when the display(s) are put to sleep after idle timeout.

[test case]

on a system with a amd gpu using the amdgpu driver, that is capable and configured for displayport mst (with multiple dp daisy chained monitors), blank the screen and then wake up the screen. This will be logged:

    [drm:generic_reg_wait [amdgpu]] *ERROR* REG_WAIT timeout 10us * 3000 tries - dce110_stream_encoder_dp_blank line:944
    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 2201 at /var/lib/dkms/amdgpu/18.50-690240/build/amd/amdgpu/../display/dc/dc_helper.c:249 generic_reg_wait+0xe7/0x160 [amdgpu]
    Call Trace:
     dce110_stream_encoder_dp_blank+0x11c/0x180 [amdgpu]
     core_link_disable_stream+0x40/0x230 [amdgpu]
     ? generic_reg_update_ex+0xdb/0x130 [amdgpu]
     dce110_reset_hw_ctx_wrap+0xb7/0x1f0 [amdgpu]
     dce110_apply_ctx_to_hw+0x30/0x430 [amdgpu]
     ? dce110_apply_ctx_for_surface+0x206/0x260 [amdgpu]
     dc_commit_state+0x2ba/0x4d0 [amdgpu]
     amdgpu_dm_atomic_commit_tail+0x297/0xd70 [amdgpu]
     ? amdgpu_bo_pin_restricted+0x58/0x260 [amdgpu]
     ? wait_for_completion_timeout+0x1f/0x120
     ? wait_for_completion_interruptible+0x1c/0x160
     commit_tail+0x3d/0x60 [drm_kms_helper]
     drm_atomic_helper_commit+0xf6/0x100 [drm_kms_helper]
     drm_atomic_connector_commit_dpms+0xe5/0xf0 [drm]
     drm_mode_obj_set_property_ioctl+0x14f/0x250 [drm]
     drm_mode_connector_property_set_ioctl+0x2e/0x40 [drm]
     drm_ioctl+0x1e0/0x430 [drm]
     ? drm_mode_connector_set_obj_prop+0x70/0x70 [drm]
     ? ep_read_events_proc+0xb0/0xb0
     ? ep_scan_ready_list.constprop.18+0x1e6/0x1f0
     ? timerqueue_add+0x52/0x80
     amdgpu_drm_ioctl+0x49/0x80 [amdgpu]
     do_vfs_ioctl+0x90/0x5f0
     SyS_ioctl+0x74/0x80
     do_syscall_64+0x74/0x140
     entry_SYSCALL_64_after_hwframe+0x3d/0xa2
    ---[ end trace 3ed7b77a97d60f72 ]---

[regression potential]

this modifies the sequence of actions during link disabling, so any regressions would appear at that time.

[other info]

this is from upstream 8c9d90eebd23b6d40ddf4ce5df5ca2b932336a06