linux-kernel - [PATCH AUTOSEL 6.12 301/486] drm/amd/display: Guard against setting dispclk low when active

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Message-Id: <20250505223922.2682012-301-sashal@kernel.org>
Date: Mon,  5 May 2025 18:36:17 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
	Gabe Teeger <gabe.teeger@....com>,
	Leo Chen <leo.chen@....com>,
	Syed Hassan <syed.hassan@....com>,
	Roman Li <roman.li@....com>,
	Daniel Wheeler <daniel.wheeler@....com>,
	Alex Deucher <alexander.deucher@....com>,
	Sasha Levin <sashal@...nel.org>,
	harry.wentland@....com,
	sunpeng.li@....com,
	christian.koenig@....com,
	airlied@...il.com,
	simona@...ll.ch,
	Charlene.Liu@....com,
	chiahsuan.chung@....com,
	alex.hung@....com,
	Nicholas.Susanto@....com,
	Ausef.Yousof@....com,
	sungjoon.kim@....com,
	PeiChen.Huang@....com,
	amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 6.12 301/486] drm/amd/display: Guard against setting dispclk low when active

From: Nicholas Kazlauskas <nicholas.kazlauskas@....com>

[ Upstream commit 72d7a7fa1f2404fd31c84a8f808b1b37021a3a9e ]

[Why]
We should never apply a minimum dispclk value while in prepare_bandwidth
or while displays are active. This is always an optimization for when
all displays are disabled.

[How]
Defer dispclk optimization until safe_to_lower = true and display_count
reaches 0.

Since 0 has a special value in this logic (ie. no dispclk required)
we also need adjust the logic that clamps it for the actual request
to PMFW.

Reviewed-by: Gabe Teeger <gabe.teeger@....com>
Reviewed-by: Leo Chen <leo.chen@....com>
Reviewed-by: Syed Hassan <syed.hassan@....com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@....com>
Signed-off-by: Roman Li <roman.li@....com>
Tested-by: Daniel Wheeler <daniel.wheeler@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 .../amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c    | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c
index 7d0d8852ce8d2..a4ac601a30c35 100644
--- a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c
+++ b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c
@@ -452,14 +452,19 @@ void dcn35_update_clocks(struct clk_mgr *clk_mgr_base,
 		update_dppclk = true;
 	}
 
-	if (should_set_clock(safe_to_lower, new_clocks->dispclk_khz, clk_mgr_base->clks.dispclk_khz)) {
+	if (should_set_clock(safe_to_lower, new_clocks->dispclk_khz, clk_mgr_base->clks.dispclk_khz) &&
+	    (new_clocks->dispclk_khz > 0 || (safe_to_lower && display_count == 0))) {
+		int requested_dispclk_khz = new_clocks->dispclk_khz;
+
 		dcn35_disable_otg_wa(clk_mgr_base, context, safe_to_lower, true);
 
-		if (dc->debug.min_disp_clk_khz > 0 && new_clocks->dispclk_khz < dc->debug.min_disp_clk_khz)
-			new_clocks->dispclk_khz = dc->debug.min_disp_clk_khz;
+		/* Clamp the requested clock to PMFW based on their limit. */
+		if (dc->debug.min_disp_clk_khz > 0 && requested_dispclk_khz < dc->debug.min_disp_clk_khz)
+			requested_dispclk_khz = dc->debug.min_disp_clk_khz;
 
+		dcn35_smu_set_dispclk(clk_mgr, requested_dispclk_khz);
 		clk_mgr_base->clks.dispclk_khz = new_clocks->dispclk_khz;
-		dcn35_smu_set_dispclk(clk_mgr, clk_mgr_base->clks.dispclk_khz);
+
 		dcn35_disable_otg_wa(clk_mgr_base, context, safe_to_lower, false);
 
 		update_dispclk = true;
-- 
2.39.5