linux-kernel - [PATCH 12/12] arm64: dts: st: add loopback clocks on LTDC node

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Message-ID: <20250725-drm-misc-next-v1-12-a59848e62cf9@foss.st.com>
Date: Fri, 25 Jul 2025 12:04:04 +0200
From: Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>
To: Yannick Fertre <yannick.fertre@...s.st.com>,
        Philippe Cornu
	<philippe.cornu@...s.st.com>,
        Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Rob Herring <robh@...nel.org>,
        Krzysztof
 Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Maxime
 Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue
	<alexandre.torgue@...s.st.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Christophe Roullier
	<christophe.roullier@...s.st.com>
CC: <dri-devel@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH 12/12] arm64: dts: st: add loopback clocks on LTDC node

ck_ker_ltdc has the CLK_SET_RATE_PARENT flag.  While having this flag is
semantically correct, it for now leads to an improper setting of the
clock rate.  The ck_ker_ltdc parent clock is the flexgen 27, which does
not support changing rates yet.  To overcome this issue, a fixed clock
can be used for the kernel clock.

Add the clocks needed for the LTDC to work.

Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>
---
 arch/arm64/boot/dts/st/stm32mp251.dtsi | 6 ++++++
 arch/arm64/boot/dts/st/stm32mp255.dtsi | 7 ++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/st/stm32mp251.dtsi b/arch/arm64/boot/dts/st/stm32mp251.dtsi
index c561df51a6001004e45fb53a56d5d42c310e6b61..54dd57e0a98eabbbcfe89459e6d63eb287f5ca04 100644
--- a/arch/arm64/boot/dts/st/stm32mp251.dtsi
+++ b/arch/arm64/boot/dts/st/stm32mp251.dtsi
@@ -52,6 +52,12 @@ clk_rcbsec: clk-rcbsec {
 			compatible = "fixed-clock";
 			clock-frequency = <64000000>;
 		};
+
+		clk_flexgen_27_fixed: clk-54000000 {
+			#clock-cells = <0>;
+			compatible = "fixed-clock";
+			clock-frequency = <54000000>;
+		};
 	};
 
 	firmware {
diff --git a/arch/arm64/boot/dts/st/stm32mp255.dtsi b/arch/arm64/boot/dts/st/stm32mp255.dtsi
index a4d965f785fa42c4597494010855aec7e1b9fdd1..82c2fa67b6b91f67d51872ed098aea897fab0197 100644
--- a/arch/arm64/boot/dts/st/stm32mp255.dtsi
+++ b/arch/arm64/boot/dts/st/stm32mp255.dtsi
@@ -5,6 +5,11 @@
  */
 #include "stm32mp253.dtsi"
 
+&ltdc {
+	clocks = <&rcc CK_BUS_LTDC>, <&clk_flexgen_27_fixed>, <&syscfg>, <&lvds>;
+	clock-names = "bus", "lcd", "ref", "lvds";
+};
+
 &rifsc {
 	lvds: lvds@...60000 {
 		compatible = "st,stm32mp25-lvds";
@@ -34,4 +39,4 @@ venc: venc@...e0000 {
 		clocks = <&rcc CK_BUS_VENC>;
 		access-controllers = <&rifsc 90>;
 	};
-};
\ No newline at end of file
+};

-- 
2.25.1