Controlling brightness in DP

[sakthikrishna.b]

Hi Team,

I want to control brightness in the DP monitor connected to Type-c port of the AGX Xavier devkit using to Type-C to DP cable.

Using the following topic as reference, I can adjust the brightness of the HDMI monitor.

If DDC/CI is supported across HDMI/DisplayPort connection

Something quite interesting (at least to me) which I just recently became aware of is that after the initial EDID query the power is disabled to the i2c for DDC for power saving. Try enabling i2c DDC power rails first before you do whatever it is you are working on: sudo echo 1 > /sys/kernel/debug/tegra_hdmi/ddc_power_toggle (disable would of course be “echo 0”)

In case of DP monitor, the ddcutil detect command is giving the output as “No displays connected” but I can see the UI in the DP monitor.

Any suggestions for debugging why DP monitor is not detected using ddcutil? and is there any other way to adjust brightness for DP displays?
@WayneWWW @JerryChang

Thanks,
Sakthi

[WayneWWW]

Only the HDMI has the ddc channel.
DP doesn’t even use the DDC channel - it uses the AUX channel

[sakthikrishna.b]

Hi @WayneWWW

I have used ddcutil to control the brightness of DP display connected using Type-C to DP cable in laptop. With the same setup I tested in AGX Xavier devkit, it was not working but it works in laptop.

Is there anything to do with AGX Xavier devkit to achieve this or Is there any other way to control brightness of DP display in AGX Xavier devkit?

Thanks,
Sakthi

[sakthikrishna.b]

Hi @WayneWWW ,

Could you please give me some pointers to look at?

Thanks,
Sakthi

[sakthikrishna.b]

Hi Team,

Could you please give me some suggestions for this? @JerryChang @WayneWWW @kayccc

Thanks,
Sakthi

[WayneWWW]

Hi,

Need some time to check this.

[sakthikrishna.b]

Hi @WayneWWW ,

I will wait for your reply.

Thanks,
Sakthi

[WayneWWW]

I have some internal discussion with display experts.

The conclusion is , unfortunately, ddcutil may not work on tegra.
We didn’t reveal the dpaux device as /dev/i2c-n in our system and ddcutil seems need those device node to do their work.

[sakthikrishna.b]

Hi @WayneWWW,

Thanks for your reply.

1. Is there any other way to control brightness in the DP display connected to AGX devkit other than ddcutil?
2. Is there any way to reveal dpaux device as /dev/i2c-n?

Thanks,
Sakthi

[sakthikrishna.b]

Hi @WayneWWW,

Could you please give some suggestions on my previous query?

Thanks,
Sakthi

[sakthikrishna.b]

Hi @WayneWWW ,

1. Is there any other way to control brightness in the DP display connected to AGX devkit other than ddcutil?
2. Is there any way to reveal dpaux device as /dev/i2c-n?

Is there any suggestions on this?

Thanks,
Sakthi

[sakthikrishna.b]

Hi @WayneWWW ,

Could you please suggest some ways to achieve this?

1. Is there any other way to control brightness in the DP display connected to AGX devkit other than ddcutil?
2. Is there any way to reveal dpaux device as /dev/i2c-n?

Thanks,
Sakthi

[WayneWWW]

Currently there is no method for it.

[WayneWWW]

Update: we have add the function to control brightness through ddcutil.

Please apply this to your kernel.ce999d0.diff.zip (1.9 KB)

[arunk]

@WayneWWW

Thanks for sharing the kernel patch.

We are able to control the DP display brightness through ddcutil after applying this kernel patch. We have tested in one DP display, will test in different monitors and share observations

Thanks,
Arun