linux-kernel - Re: [PATCH v4 10/13] arm64: dts: st: add ltdc support on stm32mp255

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Message-ID: <6dc308d7-9b31-4b6d-ba68-69a91c8fcd32@foss.st.com>
Date: Fri, 22 Aug 2025 15:05:24 +0200
From: Yannick FERTRE <yannick.fertre@...s.st.com>
To: Raphael Gallais-Pou <raphael.gallais-pou@...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: Re: [PATCH v4 10/13] arm64: dts: st: add ltdc support on stm32mp255

Hi Raphael,

Thanks for the patch.

Acked-by: Yannick Fertre <yannick.fertre@...s.st.com>

Le 21/08/2025 à 13:09, Raphael Gallais-Pou a écrit :
> Add the LTDC node for stm32mp255 SoC and handle its loopback clocks.
>
> 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.
>
> 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 | 6 ++++++
>   2 files changed, 12 insertions(+)
>
> diff --git a/arch/arm64/boot/dts/st/stm32mp251.dtsi b/arch/arm64/boot/dts/st/stm32mp251.dtsi
> index 372a99d9cc5c3730e8fbeddeb6134a3b18d938b6..b44ff221e0da968be104ff8195f9bef79c90c57a 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 f689b47c5010033120146cf1954d6624c0270045..48a95af1741c42300195b753b710e714abc60d96 100644
> --- a/arch/arm64/boot/dts/st/stm32mp255.dtsi
> +++ b/arch/arm64/boot/dts/st/stm32mp255.dtsi
> @@ -5,6 +5,12 @@
>    */
>   #include "stm32mp253.dtsi"
>   
> +&ltdc {
> +	compatible = "st,stm32mp255-ltdc";
> +	clocks = <&clk_flexgen_27_fixed>, <&rcc CK_BUS_LTDC>, <&syscfg>, <&lvds>;
> +	clock-names = "lcd", "bus", "ref", "lvds";
> +};
> +
>   &rifsc {
>   	vdec: vdec@...d0000 {
>   		compatible = "st,stm32mp25-vdec";
>