linux-kernel - [PATCH] drm/amd/display: Don't program BLNDGAM_MEM_PWR_FORCE when CM low-power is disabled on DCN30

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Message-ID: <20251020230934.387745-1-matthew.schwartz@linux.dev>
Date: Mon, 20 Oct 2025 16:09:34 -0700
From: Matthew Schwartz <matthew.schwartz@...ux.dev>
To: amd-gfx@...ts.freedesktop.org
Cc: linux-kernel@...r.kernel.org,
	mario.limonciello@....com,
	alexander.deucher@....com,
	alex.hung@....com,
	daniel.wheeler@....com,
	roman.li@....com,
	misyl@...ggi.es,
	Matthew Schwartz <matthew.schwartz@...ux.dev>
Subject: [PATCH] drm/amd/display: Don't program BLNDGAM_MEM_PWR_FORCE when CM low-power is disabled on DCN30

Before commit 33056a97ae5e ("drm/amd/display: Remove double checks for
`debug.enable_mem_low_power.bits.cm`"), dpp3_program_blnd_lut(NULL)
checked the low-power debug flag before calling
dpp3_power_on_blnd_lut(false).

After commit 33056a97ae5e ("drm/amd/display: Remove double checks for
`debug.enable_mem_low_power.bits.cm`"), dpp3_program_blnd_lut(NULL)
unconditionally calls dpp3_power_on_blnd_lut(false). The BLNDGAM power
helper writes BLNDGAM_MEM_PWR_FORCE when CM low-power is disabled, causing
immediate SRAM power toggles instead of deferring at vupdate. This can
disrupt atomic color/LUT sequencing during transitions between
direct scanout and composition within gamescope's DRM backend on
Steam Deck OLED.

To fix this, leave the BLNDGAM power state unchanged when low-power is
disabled, matching dpp3_power_on_hdr3dlut and dpp3_power_on_shaper.

Fixes: 33056a97ae5e ("drm/amd/display: Remove double checks for `debug.enable_mem_low_power.bits.cm`")
Signed-off-by: Matthew Schwartz <matthew.schwartz@...ux.dev>
---
 drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c b/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c
index 09be2a90cc79d..4f569cd8a5d61 100644
--- a/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c
+++ b/drivers/gpu/drm/amd/display/dc/dpp/dcn30/dcn30_dpp.c
@@ -578,9 +578,6 @@ static void dpp3_power_on_blnd_lut(
 			dpp_base->ctx->dc->optimized_required = true;
 			dpp_base->deferred_reg_writes.bits.disable_blnd_lut = true;
 		}
-	} else {
-		REG_SET(CM_MEM_PWR_CTRL, 0,
-				BLNDGAM_MEM_PWR_FORCE, power_on == true ? 0 : 1);
 	}
 }

-- 
2.51.1.dirty