linux-kernel - Re: [PATCH] arm64: dts: rockchip: Add DSI LCD display on rk3576-evb1

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Message-ID: <12339028.CDJkKcVGEf@phil>
Date: Mon, 20 Oct 2025 14:31:12 +0200
From: Heiko Stuebner <heiko@...ech.de>
To: Alexey Charkov <alchark@...il.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org,
 linux-kernel@...r.kernel.org,
 Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Subject: Re: [PATCH] arm64: dts: rockchip: Add DSI LCD display on rk3576-evb1

Am Montag, 20. Oktober 2025, 10:50:58 Mitteleuropäische Sommerzeit schrieb Alexey Charkov:
> 
> On Mon, Oct 20, 2025 at 12:31 PM Heiko Stuebner <heiko@...ech.de> wrote:
> >
> > Am Montag, 20. Oktober 2025, 10:19:51 Mitteleuropäische Sommerzeit schrieb Alexey Charkov:
> > > On Thu, Sep 25, 2025 at 12:38 AM Alexey Charkov <alchark@...il.com> wrote:
> > > >
> > > > Add support for the Rockchip W552793DBA-V10 LCD+touchscreen assembly which
> > > > comes physically attached to Rockchip RK3576 EVB1 boards.
> > > >
> > > > The display part is driven by the on-chip MIPI DSI controller, and the
> > > > touchscreen is connected over I2C.
> > > >
> > > > Signed-off-by: Alexey Charkov <alchark@...il.com>
> > > > ---
> > > > Note that backlight support is left out for now, as it depends on PWM
> > > > support [0] which has not yet been merged.
> > > >
> > > > A workaround is simply `gpioset -c 0 13=1` to set the respective GPIO
> > > > pin high and thus to light up the display unconditionally.
> > > >
> > > > [0] https://lore.kernel.org/lkml/20250602-rk3576-pwm-v2-0-a6434b0ce60c@collabora.com/
> > > > ---
> > > >  arch/arm64/boot/dts/rockchip/rk3576-evb1-v10.dts | 89 ++++++++++++++++++++++++
> > > >  1 file changed, 89 insertions(+)
> > >
> > > Hi Heiko,
> > >
> > > Any thoughts about this one? Can we perhaps get it merged for -next?
> >
> > Does the gpio-backlight work on that device?
> > That would make the gpioset hack unnecessary.
> 
> I've got a local patch using pwm-gpio and pwm-backlight as a stop-gap 
> solution, but I don't think it's worth merging upstream, because the 
> backlight is supposed to be driven by the hardware PWM on the same pin 
> (not bit-banging the GPIO line). After all, Nicolas has been working on 
> adding a proper hardware PWM driver for RK3576.
> 
> The display itself works without PWM support, and so does the touchscreen.

Right now, I don't think we have an actual timeline if/when Nicolas will
be able to work on the pwm again. So my idea was if we want to
integrate the baclight as you described below, to have an actual usable
display and then when the new pwm has landed switch over to that one?


Heiko


> My temp patch goes like this:
> 
> ---
>   arch/arm64/boot/dts/rockchip/rk3576-evb1-v10.dts | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/rockchip/rk3576-evb1-v10.dts 
> b/arch/arm64/boot/dts/rockchip/rk3576-evb1-v10.dts
> index f20cd6f2c079..5c27fff03569 100644
> --- a/arch/arm64/boot/dts/rockchip/rk3576-evb1-v10.dts
> +++ b/arch/arm64/boot/dts/rockchip/rk3576-evb1-v10.dts
> @@ -58,6 +58,14 @@ button-vol-up {
>   		};
>   	};
> 
> +	backlight: backlight {
> +		compatible = "pwm-backlight";
> +		brightness-levels = <20 220>;
> +		default-brightness-level = <100>;
> +		num-interpolated-steps = <200>;
> +		pwms = <&lcd_bl_pwm 0 25000 0>;
> +	};
> +
>   	hdmi-con {
>   		compatible = "hdmi-connector";
>   		type = "a";
> @@ -78,6 +86,12 @@ work_led: led-0 {
>   		};
>   	};
> 
> +	lcd_bl_pwm: pwm {
> +		#pwm-cells = <3>;
> +		compatible = "pwm-gpio";
> +		gpios = <&gpio0 RK_PB5 GPIO_ACTIVE_HIGH>;
> +	};
> +
>   	vbus5v0_typec: regulator-vbus5v0-typec {
>   		compatible = "regulator-fixed";
>   		regulator-name = "vbus5v0_typec";
> @@ -277,6 +291,7 @@ panel@0 {
>   		compatible = "wanchanglong,w552793baa", "raydium,rm67200";
>   		reg = <0>;
> 
> +		backlight = <&backlight>;
>   		iovcc-supply = <&vcc3v3_lcd_n>;
>   		reset-gpios = <&gpio3 RK_PB5 GPIO_ACTIVE_LOW>;
>   		vdd-supply = <&vcc3v3_lcd_n>;
>