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

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Message-ID: <748fd61a-31fb-436f-b028-b47807a4860c@gmail.com>
Date: Mon, 20 Oct 2025 12:50:58 +0400
From: Alexey Charkov <alchark@...il.com>
To: Heiko Stuebner <heiko@...ech.de>
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
Subject: Re: [PATCH] arm64: dts: rockchip: Add DSI LCD display on rk3576-evb1



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.

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>;
-- 

Best regards,
Alexey