drm/msm/a6xx: Fix stale rpmh votes from GPU

[ Upstream commit f561db72 ]

It was observed on sc7180 (A618 gpu) that GPU votes for GX rail and CNOC
BCM nodes were not removed after GPU suspend. This was because we
skipped sending 'prepare-slumber' request to gmu during suspend sequence
in some cases. So, make sure we always call prepare-slumber hfi during
suspend. Also, calling prepare-slumber without a prior oob-gpu handshake
messes up gmu firmware's internal state. So, do that when required.

Fixes: 4b565ca5 ("drm/msm: Add A6XX device support")
Cc: stable@vger.kernel.org
Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/639569/


Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>