drm/amd/display: Skip DPP DTO update if root clock is gated

[Why]
Hardware implements root clock gating by utilizing the DPP DTO registers
with a special case of DTO enabled, phase = 0, modulo = 1. This
conflicts with our policy to always update the DPPDTO for cases where
it's expected to be disabled.

The pipes unexpectedly enter a higher power state than expected because
of this programming flow.

[How]
Guard the upper layers of HWSS against this hardware quirk with
programming the register with an internal state flag in DCCG.

While technically acting as global state for the DCCG, HWSS shouldn't be
expected to understand the hardware quirk for having DTO disabled
causing more power than DTO enabled with this specific setting.

This also prevents sequencing errors from occuring in the future if
we have to program DPP DTO in multiple locations.

Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Jun Lei <jun.lei@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_dccg.c b/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_dccg.c
index 4c2fdfea162f..65c1d754e2d6 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_dccg.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_dccg.c
@@ -47,6 +47,14 @@ void dccg31_update_dpp_dto(struct dccg *dccg, int dpp_inst, int req_dppclk)
 {
 	struct dcn_dccg *dccg_dcn = TO_DCN_DCCG(dccg);
 
+	if (dccg->dpp_clock_gated[dpp_inst]) {
+		/*
+		 * Do not update the DPPCLK DTO if the clock is stopped.
+		 * It is treated the same as if the pipe itself were in PG.
+		 */
+		return;
+	}
+
 	if (dccg->ref_dppclk && req_dppclk) {
 		int ref_dppclk = dccg->ref_dppclk;
 		int modulo, phase;