[PATCH] drm: Add DPMS ioctl

[Daniel Stone]

Hi,

On 11 October 2017 at 08:46, Alex Ivanov <gnidorah at ya.ru> wrote:
> Display power management should be available to user no matter whether
> display server implements it or not and should be made server agnostic
> (X.Org, Wayland compositor), without need of TTY change.
>
> Reasons:
> 1. User implements an own universal power management daemon. He has no
> interest to deal with server or switch to a free TTY, he wants to
> turn off the monitor in a simple way, like he controls power of other
> system components.
> 2. Some applications under X.Org like Electron-based ones like to
> prevent screen goning off giving user no way to fix that.
> 3. Many fresh new Wayland compositors don't implement DPMS at all and
> at the same time have TTY switch broken.

I'm sorry, but this is not the right way to go about things. If Xorg
or GNOME Shell or Weston or whatever thinks the monitor is DPMS-off,
the fact that someone else has forcibly switched it back on will not
make them continue painting. Conversely, if they are painting and
someone does DPMS-off from underneath them, they'll keep painting
anyway: if they're using the legacy API that means the display will
switch straight back on, and if they're using atomic that means their
commits will suddenly fail for an unknown reason and they'll be very
confused.

If people are doing fancy new compositors without DPMS support, then I
recommend they use an existing compositor base, such as libweston
(others are also available) which actually implement DPMS. For
Electron apps, there are a number of idle-inhibition options available
for X11, and also for Wayland when that support lands in Electron.
Unfortunately I don't think there is any way to just route around the
compositor as this patch does.

Cheers,
Daniel