Unable to display a splash screen during u-boot startup on sam9x60_curiosity

[gbmbg]

Good evening, I'm tryng to adapt this procedure:
https://developerhelp.microchip.com/xwiki/bin/view/applications/linux4sam/faq/boot-logo/
to our case, a custom board based on sam9x60_curiosity with a pda5000 LCD display.
Everithyng works fine under linux kernel, but inside u-boot the atmel_hlcdfb is not probed...

Here are the DTS snippets employed

/ {

backlight: backlight {
	compatible = "pwm-backlight";
	pwms = <&hlcdc_pwm 0 50000 0>;
	brightness-levels = <0 4 8 16 32 64 128 255>;
	default-brightness-level = <7>;
	power-supply = <&bl_reg>;
	status = "okay";
	u-boot,dm-pre-reloc;
};

bl_reg: backlight_regulator {
	compatible = "regulator-fixed";
	regulator-name = "backlight-power-supply";
	regulator-min-microvolt = <5000000>;
	regulator-max-microvolt = <5000000>;
	status = "okay";
	u-boot,dm-pre-reloc;
};

panel: panel {
	compatible = "simple-panel";
	backlight = <&backlight>;
	power-supply = <&panel_reg>;
	status = "okay";
	connector-type = "rgb";
	u-boot,dm-pre-reloc;

	panel-timing {
		clock-frequency = <33300000>;   // 33.3 MHz
		hactive = <800>;
		vactive = <480>;
		hsync-len = <64>;
		hfront-porch = <1>;
		hback-porch = <64>;
		vsync-len = <23>;
		vfront-porch = <1>;
		vback-porch = <22>;
		hsync-active = <1>;
		vsync-active = <1>;
		de-active = <1>;        // tipico TFT
		pixelclk-active = <0>;  // campiona sul fronte neagativo (se richiesto dal pannello)
		u-boot,dm-pre-reloc;
	};

port@0 {
		u-boot,dm-pre-reloc;
		panel_input: endpoint@0 {
			remote-endpoint = <&hlcdc_panel_output>;
			u-boot,dm-pre-reloc;
		};
	};
};

panel_reg: panel_regulator {
    compatible = "regulator-fixed";
    regulator-name = "panel-power-supply";
    regulator-min-microvolt = <3300000>;
    regulator-max-microvolt = <3300000>;
    status = "okay";
	u-boot,dm-pre-reloc;
};

hlcdc: hlcdc@f8038000 {
	compatible = "microchip,sam9x60-hlcdc",atmel,at91sam9x5-hlcdc";
	reg = <0xf8038000 0x4000>;
	interrupts = <25 IRQ_TYPE_LEVEL_HIGH 0>;
	clocks = <&pmc PMC_TYPE_PERIPHERAL 25>, <&pmc PMC_TYPE_GCK 25>, <&slow_xtal>;
	clock-names = "periph_clk","sys_clk", "slow_clk";
	assigned-clocks = <&pmc PMC_TYPE_GCK 25>;
	assigned-clock-parents = <&pmc PMC_TYPE_CORE 10>;
	atmel,vl-bpix = <5>;            // RGB888 (24 bpp)
	atmel,guard-time = <1>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_lcd_base &pinctrl_lcd_pwm &pinctrl_lcd_rgb666>;
	status = "okay";
	u-boot,dm-pre-reloc;

		hlcdc-display-controller {
			// Collega il controller al pannello via endpoint
			compatible = "atmel,hlcdc-display-controller";
			#address-cells = <1>;
			#size-cells = <0>;
			u-boot,dm-pre-reloc;
			port@0 {
				#address-cells = <1>;
				#size-cells = <0>;
				reg = <0>;
				u-boot,dm-pre-reloc;
				hlcdc_panel_output: endpoint@0 {
					u-boot,dm-pre-reloc;
					remote-endpoint = <&panel_input>;
				};
			};
		};

		// PWM del backlight sull’uscita HLCDC, pinmux PIOC26
		hlcdc_pwm: hlcdc-pwm {
			compatible = "atmel,hlcdc-pwm";
			#pwm-cells = <3>;
			pinctrl-names = "default";
			pinctrl-0 = <&pinctrl_lcd_pwm>;
			u-boot,dm-pre-reloc;
		};
	};

[...]

&pinctrl {

lcd {
	pinctrl_lcd_base: lcd-base-0 {
		u-boot,dm-pre-reloc;
		atmel,pins = <AT91_PIOC 27 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDVSYNC */
			      AT91_PIOC 28 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDHSYNC */
			      AT91_PIOC 24 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDDISP */
			      AT91_PIOC 29 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDDEN */
			      AT91_PIOC 30 AT91_PERIPH_A AT91_PINCTRL_NONE>;	/* LCDPCK */
	};

	pinctrl_lcd_rgb666: lcd-rgb-2 {
		u-boot,dm-pre-reloc;
		atmel,pins = <AT91_PIOC 2 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD2 pin */
			      AT91_PIOC 3 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD3 pin */
			      AT91_PIOC 4 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD4 pin */
			      AT91_PIOC 5 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD5 pin */
			      AT91_PIOC 6 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD6 pin */
			      AT91_PIOC 7 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD7 pin */
			      AT91_PIOC 10 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD10 pin */
			      AT91_PIOC 11 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD11 pin */
			      AT91_PIOC 12 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD12 pin */
			      AT91_PIOC 13 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD13 pin */
			      AT91_PIOC 14 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD14 pin */
			      AT91_PIOC 15 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD15 pin */
			      AT91_PIOC 18 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD18 pin */
			      AT91_PIOC 19 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD19 pin */
			      AT91_PIOC 20 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD20 pin */
			      AT91_PIOC 21 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD21 pin */
			      AT91_PIOC 22 AT91_PERIPH_A AT91_PINCTRL_NONE	/* LCDD22 pin */
			      AT91_PIOC 23 AT91_PERIPH_A AT91_PINCTRL_NONE>;	/* LCDD23 pin */
	};

	pinctrl_lcd_pwm: lcd_pwm {
		u-boot,dm-pre-reloc;
		atmel,pins = <AT91_PIOC 26 AT91_PERIPH_A AT91_PINCTRL_NONE>;
	};
};

};

Any help would be very appreciated
Thanks a lot and work well
Giovanni

[varshini-rajendran]

Hi @gbmbg ,

Apologies for the delay in response. I am currently trying to reproduce this scenario at my end. Meanwhile can you specify some details like the version of u-boot used etc? I am trying on the latest version of u-boot (2025.07) branch - u-boot-2025.07-mchp. I will let you know as soon as I have more information.

Thank you for your patience.

Regards,
Varshini Rajendran.

[gbmbg]

Hi @varshini-rajendran,
no worries and thanks a lot for your reply.
I’m currently using:
U-Boot 2024.07-linux4microchip-2024.10

If migration to the new version is required, I’ll proceed with that.

Thanks again and have a nice day
Giovanni Battista Montanari (GB)

[varshini-rajendran]

Hi @gbmbg ,

I have reproduced the issue on my side and investigated it. Seems that the sam9x60 does not support splash screen display by default. There are some other changes in addition to the documentation that are needed. The reason why the driver did not probe for you is that the logo display function is not called from the board file. I am attaching the patches as a zip in here. Please try it at your end. In the meantime the patch will be (is already) under review in our local mailing list, after which the support will be pushed to the repo.

I tested this with the latest u-boot-2025.07-mchp (linux4microchip-2025.10 tag). But it should work the same way in 2024.10 tag as well.

Be aware that these patches contains only the basic support of a splash screen. I have not included any additional data that you've pasted above. Please feel free to build it on top of this.

0001-video-atmel-add-support-for-sam9x60-hlcdc.patch

0002-board-sam9x60_curiosity-add-support-to-display-boot-.patch

0003-ARM-dts-at91-sam9x60_curiosity-add-hlcdc-and-display.patch

Please do not hesitate to come back with questions.

[gbmbg]

Hi @varshini-rajendran ,
thanks a lot for the detailed explanation and for sharing the patches.

In the next days I will test everything on my side and let you know the results as soon as I can.

Thanks again, and have a nice weekend!

[gbmbg]

Hi @varshini-rajendran,
I tested your patches reverting on a clean U-Boot 2024.07-linux4microchip-2024.10 installation and they work very well — I can now see both the Microchip U‑Boot logo and my custom BMP image.
Thanks a lot for your support!

Unfortunately, when Linux starts I get visible flickering on the LCD.
I’m still using linux4microchip‑2024.10 for both U‑Boot and Linux, with a custom sam9x60 Curiosity overlay based on the one you provide for pda5000.

Here is the relevant part of my DTSo:

[...]

&hlcdc {
status = "okay";

hlcdc-display-controller {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_lcd_base &pinctrl_lcd_rgb666>;
	port@0 {
		#address-cells = <1>;
		#size-cells = <0>;
		hlcdc_panel_output: endpoint@0 {
			reg = <0>;
			remote-endpoint = <&panel_input>;
		};
	};
};

hlcdc_pwm: hlcdc-pwm {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_lcd_pwm>;
};

};
[...]
&{/}{
backlight: backlight {
compatible = "pwm-backlight";
pwms = <&hlcdc_pwm 0 50000 0>;
brightness-levels = <0 4 8 16 32 64 128 255>;
default-brightness-level = <7>;
power-supply = <&bl_reg>;
status = "okay";
};

bl_reg: backlight_regulator {
	compatible = "regulator-fixed";
	regulator-name = "backlight-power-supply";
	regulator-min-microvolt = <5000000>;
	regulator-max-microvolt = <5000000>;
	status = "okay";
};

panel: panel {
	compatible = "pda,91-00156-a0", "simple-panel";	
	backlight = <&backlight>;
	power-supply = <&panel_reg>;
	#address-cells = <1>;
	#size-cells = <0>;
	status = "okay";
	connector-type = "dsi";

	port@0 {
		reg = <0>;
		#address-cells = <1>;
		#size-cells = <0>;

		panel_input: endpoint@0 {
			reg = <0>;
			remote-endpoint = <&hlcdc_panel_output>;
		};
	};
};

panel_reg: panel_regulator {
	compatible = "regulator-fixed";
	regulator-name = "panel-power-supply";
	regulator-min-microvolt = <3300000>;
	regulator-max-microvolt = <3300000>;
	status = "okay";
};

};

Since U‑Boot shows the image perfectly (no flicker at all), it seems the issue appears only when the Linux HLCDC driver takes over,
maybe re‑initializing HLCDC with slightly different timing or polarity.

Do you have any recommended settings or alignment notes for the HLCDC handover between U‑Boot and Linux?
Or any known adjustments needed when enabling HLCDC in U‑Boot?

Thanks again, and Merry Christmas!

[varshini-rajendran]

Hi @gbmbg ,

Can you try the patch pasted below ? Apply the patch in linux to avoid this flickering issue. You are right and this patch will take care of the clock and backlight re-init.

diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
index a527badf865d..6a08afe448df 100644
--- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
+++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
@@ -526,12 +526,18 @@ static void update_hlcdc_buffers(struct atmel_hlcdc_plane *plane,
struct atmel_hlcdc_plane_state *state,
u32 sr, int i)
{
+ static int force_update = 1;
+
atmel_hlcdc_layer_write_reg(&plane->layer,
 ATMEL_HLCDC_LAYER_PLANE_HEAD(i),
 state->dscrs[i]->self);
- if (sr & ATMEL_HLCDC_LAYER_EN)
- return;
+ if (unlikely(force_update))
+ force_update = 0;
+ else {
+ if (sr & ATMEL_HLCDC_LAYER_EN)
+ return;
+ }
atmel_hlcdc_layer_write_reg(&plane->layer,
 ATMEL_HLCDC_LAYER_PLANE_ADDR(i),
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index c0523a0269ee..fbb16cafdf04 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -533,6 +533,9 @@ static int pwm_backlight_probe(struct platform_device *pdev)
if (!state.period && (data->pwm_period_ns > 0))
state.period = data->pwm_period_ns;
+ state.enabled = 1;
+ state.duty_cycle = 50000;
+
ret = pwm_apply_state(pb->pwm, &state);
if (ret) {
dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n",

Please beware, this patch might not get applied as such. Do get back if you have further queries.

Have a Happy New Year !

Thanks,
Varshini Rajendran.

[gbmbg]

Hi @varshini-rajendran,

thanks a lot for the detailed reply and for the patches, and happy new year to you too!
I’ve taken your two diffs and turned them into proper kernel patches.
Unfortunately, with these two patches in place, the behaviour on my board is essentially unchanged:

• the U‑Boot splash screen is perfectly stable
• the flicker appears exactly when Linux takes over
• the two patches (HLCDC plane + PWM backlight) do not remove or reduce the flicker in my setup

If you have an internal setup where these patches remove the flicker, could you please share:

• the exact Linux version / linux4microchip tag you tested on
• the relevant DT snippets for the panel, backlight and HLCDC

That would help me understand what might be different in my case and how to align with your working configuration.

Thanks again for your time and support.
Have a nice day!
Giovanni Battista