AM6548: Brightness issue of PWM backlight

wan kun

Part Number: AM6548

Hi ,

We are adjusting the PWM backlight and found that setting the brightness to 0 is the same as setting it to 8, which are the brightest, but setting the brightness to 1 to 7 is normal.

That is, setting the brightness to 0 and changing the bl_power setting of the backlight to "1". You can't turn off the backlight. Have you encountered similar problems?

Its related setting in DTS list as follow:

Fullscreen

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......
lcd_bl: backlight {
            compatible = "pwm-backlight";
                pwms = <&ehrpwm1 0 5000000 PWM_POLARITY_INVERTED>;
                brightness-levels =
                        <0 32 64 96 128 160 192 224 255>;
                default-brightness-level = <5>;
        };
......
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

......
lcd_bl: backlight {
        	compatible = "pwm-backlight";
                pwms = <&ehrpwm1 0 5000000 PWM_POLARITY_INVERTED>;
                brightness-levels =
                       	<0 32 64 96 128 160 192 224 255>;
                default-brightness-level = <5>;
        };
......

Thanks

Kenn

over 3 years ago

0 Hong Guan64 over 3 years ago

TI__Guru 65135 points

Hello, the subject owner is currently out of office, and please expect a delayed response some time next week.

0 wan kun over 3 years ago in reply to Hong Guan64

Prodigy 215 points

Hello, any update about this issue?

Thanks

Kenn

0 Nick Saulnier over 3 years ago in reply to wan kun

TI__Guru* 93345 points

Hello Kenn,

Apologies for the delayed response. To confirm, are you trying to totally turn off the screen with the command?

I do not have a board to run tests on at this point in time. However, I wonder if ID_BACKLIGHT_CLAMP could be having an impact in clamping the brightness to be at least 5% (or the same as the brightness for 1). See this discussion about an older release of AM335x software: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/680308/linux-am3354-lcd-backlight-control-issue/2521771#2521771

Regards,

Nick

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AM6548: Brightness issue of PWM backlight