Re: [PATCH v2 2/5] acpi/x86: s2idle: handle Display On/Off calls outside of suspend sequence

[Mario Limonciello <mario.limonciello@amd.com>]

On 9/23/2024 11:15, Antheas Kapenekakis wrote:
> Does DRM core handle virtual displays like VNC?
> 

You can make use of virtual display connectors in amdgpu.  This is how 
drivers for new ASICs are first developed in emulation and also what's 
used for early hardware bring up.

You can see virtual_display from 
https://www.kernel.org/doc/html/v6.11/gpu/amdgpu/module-parameters.html 
for more details.

> As mentioned in the cover letter, the _DSM specifies both virtual and
> actual displays.
> 
> Also, Windows behavior is like a lockscreen. 5 seconds after screen
> turns off after inactivity, instantly when you press the power button.
> 
> I tend towards making a sysfs entry. Not sure.
> 

Who would call this sysfs file?  Systemd?  The compositor?  When?

In Linux the compositor is in charge of doing the modesets that involve 
turning on/off the screen.  In most cases if you press the power button 
in Linux systemd-logind picks up the event.  It triggers a behavior 
that's controlled by the logind configuration.  Typically that's turning 
on a lockscreen and/or starting the suspend sequence.

Important to note; it DOESN'T explicitly turn off displays.  If you 
configured it to suspend then displays get turned off as part of the 
kernel suspend sequence (drm_atomic_helper_disable_all).

If it is configured to trigger a lockscreen then the compositor will 
turn off displays after whatever the DPMS configuration is set to.