Display flickering when set to lower brightness

[fsong1]

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

[praveen_adi]

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. 

[fsong1]

Hello,

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

Best regards,

Frank

[Bio_TICFSL]

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...

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

[fsong1]

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