i.MX ProcessorsのトピックRe: Display flickering when set to lower brightness

Display flickering when set to lower brightness

fsong1 — Tue, 30 Jul 2024 08:50:04 GMT

Hello,

I'm using i.MX8M Mini EVK and rm67199 panel, and original evk-rm67199.dtb for the board. After board bootup, the default display of weston-desktop-shell looks fine, no blink and no flicker.

Under a special scenario, we need a lower level of brightness. Adjust the brightness from normal value 255 to lower value such as 150, using the command:

# echo 150 > /sys/devices/platform/soc@0/32c00000.bus/32e10000.mipi_dsi/32e10000.mipi_dsi.0/backlight/32e10000.mipi_dsi.0/brightness

The screen becomes not bright as before. This is what I expected. But it is flickering. And lower value of brightness, higher frequency of flicker.

So any tips on this?

Thanks,

Frank

Re: Display flickering when set to lower brightness

Bio_TICFSL — Tue, 30 Jul 2024 14:35:41 GMT

Hello,

Which image are you using on your setup? Please try the latest bsp should come with default image, did you make tests only using the one you generated or with the default one too?

I made a small test here flashing the most recent reference multimedia image and it worked as expected, the brightness changes according to the values provided on https://git.toradex.com/cgit/linux-toradex.git/tree/arch/arm64/boot/dts/freescale/imx8mm-verdin.dtsi?h=toradex_5.4-2.3.x-imx#n22

of the device tree backlight node. After flashing the image the only modification I did is writing the correct .dtbo

I made this with the EVK and kernel 5.1.15.

Regards

Re: Display flickering when set to lower brightness

fsong1 — Wed, 31 Jul 2024 02:45:44 GMT

Hello,

Thanks a lot for your support. We are using mickledore release (kernel 6.1.22), and the multimedia image we generated for the EVK board.

The backlight node in device tree is as below (the entire dts file is attached):

backlight: backlight {
compatible = "pwm-backlight";
pwms = <&pwm1 0 5000000 0>;
brightness-levels = <0 255>;
num-interpolated-steps = <255>;
default-brightness-level = <250>;
};

I can see the screen brightness changes with different settings of brightness value. The issue is, when set lower brightness value, e.g 120, there are obvious display flickers.

It is OLED panel. I'm not clear if more need done for setting brightness. I just input the command for this:

# echo 120 > /sys/devices/platform/soc@0/32c00000.bus/32e10000.mipi_dsi/32e10000.mipi_dsi.0/backlight/32e10000.mipi_dsi.0/brightness

Regards,

Frank

Re: Display flickering when set to lower brightness

praveen_adi — Wed, 31 Jul 2024 20:59:13 GMT

Hi @fsong1 , The brightness-levels is an array(separated by spaces) and not a range. Pls refer to the https://www.kernel.org/doc/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt for additional information on the parameters.

In your dts file configuration, 120 is not defined.

Re: Display flickering when set to lower brightness

fsong1 — Thu, 01 Aug 2024 07:38:45 GMT

Hello,

Thanks a lot for your advice. Let me look into the linked documentation.

Best regards,

Frank