drm/amd/display: Disable PG on NV12

[Why]
According to HW team, PG is dropped for NV12, but programming
the registers will still cause power to be consumed, so don't
program for NV12.

[How]
Set function pointer to NULL if NV12
Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c

@@ -1268,7 +1268,8 @@ void dcn10_init_hw(struct dc *dc)
 		}
 
 		//Enable ability to power gate / don't force power on permanently
-		hws->funcs.enable_power_gating_plane(hws, true);
+		if (hws->funcs.enable_power_gating_plane)
+			hws->funcs.enable_power_gating_plane(hws, true);
 
 		return;
 	}
@@ -1385,8 +1386,8 @@ void dcn10_init_hw(struct dc *dc)
 
 		REG_UPDATE(DCFCLK_CNTL, DCFCLK_GATE_DIS, 0);
 	}
-
-	hws->funcs.enable_power_gating_plane(dc->hwseq, true);
+	if (hws->funcs.enable_power_gating_plane)
+		hws->funcs.enable_power_gating_plane(dc->hwseq, true);
 
 	if (dc->clk_mgr->funcs->notify_wm_ranges)
 		dc->clk_mgr->funcs->notify_wm_ranges(dc->clk_mgr);

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c

@@ -3760,6 +3760,15 @@ static bool dcn20_resource_construct(
 
 	dcn20_hw_sequencer_construct(dc);
 
+	// IF NV12, set PG function pointer to NULL. It's not that
+	// PG isn't supported for NV12, it's that we don't want to
+	// program the registers because that will cause more power
+	// to be consumed. We could have created dcn20_init_hw to get
+	// the same effect by checking ASIC rev, but there was a
+	// request at some point to not check ASIC rev on hw sequencer.
+	if (ASICREV_IS_NAVI12_P(dc->ctx->asic_id.hw_internal_rev))
+		dc->hwseq->funcs.enable_power_gating_plane = NULL;
+
 	dc->caps.max_planes =  pool->base.pipe_count;
 
 	for (i = 0; i < dc->caps.max_planes; ++i)