drm/amd/display: hold a vblank ref while writeback is pending

Writeback completion is detected in dm_crtc_high_irq(), the CRTC vblank
IRQ handler. The arm path (dm_set_writeback) never took a vblank
reference, so the interrupt was only enabled incidentally (by a pageflip
on the same commit, fbcon, or a previous vblank's off-delay window).

A writeback-only commit right after a fresh drm_crtc_vblank_on() (e.g. a
writeback connector detached and re-attached) therefore has no vblank
reference: the IRQ never fires, wb_pending is never cleared and the out
fence times out. This is reproducible with IGT kms_writeback and was
seen via kms_colorop on writeback-capable hardware. The relevant IGT
branch is at
https://gitlab.freedesktop.org/hwentland/igt-gpu-tools/-/tree/yuv-fm-colorop

Take a vblank reference when arming the writeback and release it once
completion is signalled. The get is done before arming wb_pending so the
completion IRQ cannot drop the reference before it is taken. Factor the
shared completion bookkeeping into amdgpu_dm_crtc_complete_writeback()
and also call it from the teardown path, so a writeback torn down while
still pending signals its out fence and releases the reference instead of
leaking both.

Fixes: c81e13b929df ("drm/amd/display: Hande writeback request from userspace")
Assisted-by: Copilot:claude-opus-4.8
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: George Zhang <george.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

0 files changed, 0 insertions, 0 deletions