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

["Heiko Stübner" <heiko@sntech.de>]

Am Montag, 20. Oktober 2025, 14:31:12 Mitteleuropäische Sommerzeit schrieb Heiko Stuebner:
> 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@sntech.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@gmail.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@gmail.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?

With the ELCE around the corner we're nearing the year-mark here ;-)
(And I'm surprised, I remembered this pending patch)

So how about integrating your gpio-pwm backlight for the time being?

Or alternatively just going with a gpio-backlight, like the Anbernic Vita did:

        /*
         * LEDs and Backlights can be controlled as a PWM, but PWM
         * support is not yet available.
         */
        gpio_backlight: backlight {
                compatible = "gpio-backlight";
                gpios = <&gpio2 RK_PC4 GPIO_ACTIVE_HIGH>;
                pinctrl-0 = <&led_backlight_h>;
                pinctrl-names = "default";
        };

DSI without backlight is a quite black screen, which I'd call non-working
still, so would require some form of backlight.


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>;
> > 
> 
>