[ Upstream commit 428da2bdb05d76c48d0bd8fbfa2e4c102685be08 ]

[Why]
In order to read CRC events when CRC capture is enabled the vblank
interrput handler needs to be running for the CRTC. The handler is
enabled while there is an active vblank reference.

When running IGT tests there will often be no active vblank reference
but the test expects to read a CRC value. This is valid usage (and
works on i915 since they have a CRC interrupt handler) so the reference
to the vblank should be grabbed while capture is active.

This issue was found running:

igt@kms_plane_multiple@atomic-pipe-b-tiling-none

The pipe-b is the only one in the initial commit and was not previously
active so no vblank reference is grabbed. The vblank interrupt is
not enabled and the test times out.

[How]
Keep a reference to the vblank as long as CRC capture is enabled.
If userspace never explicitly disables it then the reference is
also dropped when removing the CRTC from the context (stream = NULL).
Signed-off-by: NNicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: NHarry Wentland <Harry.Wentland@amd.com>
Reviewed-by: NSun peng Li <Sunpeng.Li@amd.com>
Acked-by: NLeo Li <sunpeng.li@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>