[bitanarch]

You can enable, yes. But (assuming you're on an LCD display and not an OLED), you're likely still on XRGB8888 - i.e. 8-bit per channel. Check `drm_info`.

Also, go to YouTube and play this video: https://www.youtube.com/watch?v=onVhbeY7nLM

Do it once on "HDR" on Linux, and then on Windows. The "HDR" in nVidia/Linux is fake.

The brightness you see on Plasma or Mutter is indeed related to the HDR support in the driver. But - it's not really useful for the most common HDR tasks at the moment.

[EnPissant]

I asked claude to investigate:

  Your Display Configuration

  Both monitors are outputting 10-bit color using the ABGR2101010 pixel format.

  | Monitor                | Connector | Format      | Color Depth | HDR          | Colorspace |
  |------------------------|-----------|-------------|-------------|--------------|------------|
  | Dell U2725QE (XXXXXXX) | HDMI-A-1  | ABGR2101010 | 10-bit      | Enabled (PQ) | BT2020_RGB |
  | Dell U2725QE (XXXXXXX) | HDMI-A-2  | ABGR2101010 | 10-bit      | Disabled     | Default    |

* Changed the serial numbers to XXXXXXX

I am on Wayland and outputting via HDMI 2.1 if that helps.

EDIT: Claude explained how it determined this with drm_info, and manually verified it:

> Planes 0 and 3 are the primary planes (type=1) for CRTCs 62 and 81 respectively - these are what actually display your desktop content. The Format: field shows the pixel format of the currently attached framebuffer.

EDIT: Also note that I am slowbanned on this site, so may not be able to respond for a bit.

EDIT: You should try connecting with HDMI 2.1 (you will need a 8k HDMI cable or it will fall back to older standards instead of FRL).

EDIT: HDR on youtube appears to work for me. Youtube correctly indentifies HDR on only 1 of my monitors and I can see a big difference in the flames between them on this scene: https://www.youtube.com/watch?v=WjJWvAhNq34

[bitanarch]

I don't have a Dell U2725QE, but on InnoCN 27M2V and Cooler Master GP27U there's no ABGR2101010 support. These monitors would only work with ARGB2101010 or XRGB2101010 which nVidia drivers do not provide.

Here's what I'm getting on both monitors, with HDR enabled on Gnome 49: https://imgur.com/a/SCyyZWt

Maybe you're lucky with the Dell. But as I understand, HDR playback on Chrome is still broken.

[bitanarch]

Ok. I've been using DisplayPort 1.4a with my 4090 at the moment. Maybe I'll try HDMI 2.1 and see what happens.

I'm actually surprised that YouTube HDR works on your side - perhaps it's tied to the ABGR2101010 output mode being available.

[EnPissant]

It's not obvious how to interpret the output. I pasted it into chatgpt and it thinks I am using "Format: ABGR2101010" for both monitors (only 1 has HDR on) so I don't trust it.

EDIT: See my sibling comment.

[bitanarch]

Under the Planes section, look for planes that have non-zero "CRTC_ID". Those are the planes that actually get output to your monitor.

Here's what I'm getting on an RTX 4090 / InnoCN 27M2V and Cooler Master Tempest GP27U.

https://imgur.com/a/SCyyZWt