PTN3460 eDP pwm control: not supported?

[nikolaus_voss]

Hi,

I want to use pwm brightness control over eDP DPCD register, however the capability registers read:

0x701 = 01

0x702 = 85

which according to the eDP specs means that DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP is set instead of DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP.

Chapter 8.3.2 of datasheet says that

"PWMO pin — the PWM signal generated by PTN3460 based on controls set in
DPCD registers. In addition, PTN3460 can pass through PWM signal from eDP
source as well. Please refer to Ref. 2 for more information."
However, Ref. 2 doesn't clarify this. It seems that PWM pass through is the default. How can I change that?

Regards,

Nikolaus Voss

[nikolaus_voss]

Hi,

any update on this? How can I program the PWM via DPCD register?

Regards,

Nikolaus

[nikolaus_voss]

Update: Writing PWM specs to DPCD-registers works, PTN3460 simply reports wrong capabilities.

Can PTN3460 be fixed to comply with eDP spec?

[TomasVaverka]

Hi Nikolaus,

Please see below figure and attached PTN3460I AN11606 (programming guide). “PWM pass through” is disabled by default.

Best regards,

Tomas

[nikolaus_voss]

Hi Tomas,

thanks for your answer. So why is DPCD reg 0x702 set to 85 then? I use PTN3460 on linux along with the intel_dp_aux_backlight.c driver (part of i915 driver). It refuses to work with this register content as DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP is not set. How can this DPCD register be influenced? Are there any linux drivers known to work with brightness setting over AUX channel?

Regards,

Nikolaus