linux-kernel - [PATCH 1/2] arm64: dts: qcom: sm8550: correct MDSS interconnects

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Message-Id: <20241008-fix-sm8x50-mdp-icc-v1-1-77ffd361b8de@linaro.org>
Date: Tue, 08 Oct 2024 02:36:59 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Bjorn Andersson <andersson@...nel.org>, 
 Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Neil Armstrong <neil.armstrong@...aro.org>
Cc: Abhinav Kumar <quic_abhinavk@...cinc.com>, 
 Rob Clark <robdclark@...il.com>, 
 Marijn Suijten <marijn.suijten@...ainline.org>, 
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, freedreno@...ts.freedesktop.org, 
 stable@...nel.org
Subject: [PATCH 1/2] arm64: dts: qcom: sm8550: correct MDSS interconnects

SM8550 lists two interconnects for the display subsystem, mdp0-mem
(between MDP and LLCC) and mdp1-mem (between LLCC and EBI, memory).
The second interconnect is a misuse. mdpN-mem paths should be used for
several outboud MDP interconnects rather than the path between LLCC and
memory. This kind of misuse can result in bandwidth underflows, possibly
degradating picture quality as the required memory bandwidth is divided
between all mdpN-mem paths (and LLCC-EBI should not be a part of such
division).

Drop the second path and use direct MDP-EBI path for mdp0-mem until we
support separate MDP-LLCC and LLCC-EBI paths.

Fixes: d7da51db5b81 ("arm64: dts: qcom: sm8550: add display hardware devices")
Cc: stable@...nel.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
---
 arch/arm64/boot/dts/qcom/sm8550.dtsi | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/boot/dts/qcom/sm8550.dtsi b/arch/arm64/boot/dts/qcom/sm8550.dtsi
index 9dc0ee3eb98f..cca10f9faa14 100644
--- a/arch/arm64/boot/dts/qcom/sm8550.dtsi
+++ b/arch/arm64/boot/dts/qcom/sm8550.dtsi
@@ -2871,9 +2871,8 @@ mdss: display-subsystem@...0000 {
 
 			power-domains = <&dispcc MDSS_GDSC>;
 
-			interconnects = <&mmss_noc MASTER_MDP 0 &gem_noc SLAVE_LLCC 0>,
-					<&mc_virt MASTER_LLCC 0 &mc_virt SLAVE_EBI1 0>;
-			interconnect-names = "mdp0-mem", "mdp1-mem";
+			interconnects = <&mmss_noc MASTER_MDP 0 &mc_virt SLAVE_EBI1 0>;
+			interconnect-names = "mdp0-mem";
 
 			iommus = <&apps_smmu 0x1c00 0x2>;
 

-- 
2.39.5