Subject: VESA DDC/CI display backlight

From: Alexander GamePad <[email-masked]>
Date: Sun, 8 Sep 2013 21:52:26 +0400

Well, this is a feature that is presents in most displays, but is  hardly
ever used by software.

Xorg could handle backlight of notebook displays, but not of standalone
displays.

There is a project called ddccontrol: http://ddccontrol.sourceforge.net/
The core of this project is not really tough to implement inside Mir,
because it is just a simple wrapper of I2C protocol.

Practical usage:
- Unified backlight interface (ACPI from notebooks, DDC/CI, maybe, HDMI)
- Ability to control display backlight from System Settings, xbacklight
(well, mirbacklight, of course ;) ) and from any other display tool.
- Ability to create such a cool feature as automatic backlight (using a
webcam).

So, is there a possibility to include DDC support in Mir?

---

From: Daniel van Vugt <[email-masked]>
Date: Tue, 10 Sep 2013 09:33:50 +0800

Alexander,

If it's part of DDC then certainly Mir might be the place to implement 
that. I don't think it's a high priority for the team in 13.10 though.

Maybe it should be discussed as part of:
https://bugs.launchpad.net/xmir/+bug/1211797
?

- Daniel

On 09/09/13 01:52, Alexander GamePad wrote:
> Well, this is a feature that is presents in most displays, but is
> hardly ever used by software.
>

---

From: Alexander GamePad <[email-masked]>
Date: Sat, 14 Sep 2013 14:47:11 +0400

Daniel,

Well, I checked out linux backlight infrastructure, and I understood, that
backlight controls are lower level than Mir.

We need a universal solution, that could work with Mir or even in console
mode.

Maybe, smb could write a library, that tries to control backlight level
using several ways (just like libbacklight, but more advanced) and make Mir
to use it?

I propose such ways (higher is preferred):
- Firmware (for LVDS)
- Platform (linux native)
- DDC/CI (for displays, that support such thing)
- Raw (for controlling devices using PCI interace)
- Display server interface for changing picture brightness (it is a
fallback way to control displays or GPUs that support none of the ways
above. Redshift tool could do such thing using XRandr).

In the case of yes, I am ready to write such library and tool with
xbacklight-like CLI.

But this library will use system functions extensively, so root permissions
are required (or a daemon part started on boot).
Alexander,

Maybe it should be discussed as part of:
https://bugs.launchpad.net/**xmir/+bug/1211797<https://bugs.launchpad.net/xmir/+bug/1211797>
?

- Daniel

On 09/09/13 01:52, Alexander GamePad wrote:

> There is a project called ddccontrol: http://ddccontrol.sourceforge.**net/<http://ddccontrol.sourceforge.net/>