Re: acpivga(4) v. MI display controls

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On 15.10.10 01:50, David Young wrote:
> It's important to be able to control display switching and brightness,
> but I don't think that those functions should reside in acpivga(4) and
> acpiout(4) devices under acpi(4).  For example, I read in somebody's
> dmesg today:
> 
> acpivga0 at acpi0 (GFX0): ACPI Display Adapter
> acpiout0 at acpivga0 (CRT1, 0x0100): ACPI Display Output Device
> acpiout1 at acpivga0 (DTV1, 0x0200): ACPI Display Output Device
> acpiout2 at acpivga0 (LCD, 0x0400): ACPI Display Output Device
> acpivga0: connected output devices:
> acpivga0:   0x0100 (acpiout0): Ext. Monitor, head 0, bios detect
> acpivga0:   0x0200 (acpiout1): TV, head 0, bios detect
> acpivga0:   0x0400 (acpiout2): Unknown Output Device, head 0, bios detect
> 
> Rather than attaching new nodes at acpi0, the system should let ACPI
> BIOS inform the autoconfiguration process, which should attach one or
> more instances of a new, MI device, display(4).  For example:
> 
> vga0 at pci0 device ... function ...
> display0 at vga0: Ext. Monitor, head 0, bios detect (ACPI CRT1)
> display1 at vga0: TV, head 0, bios detect (ACPI DTV1)
> display2 at vga0: Unknown Output Device, head 0, bios detect (ACPI LCD)
> 
> No nodes acpivga0..N or acpiout0..N should be attached.
> 
> Each display(4) exists for reading information about its corresponding
> display, such as EDID; for activating power-saving modes on the display;
> for changing the display brightness; and for turning the display on and
> off.  In principle, display(4) can use methods provided either by a
> non-ACPI BIOS or by a NetBSD driver that accesses the hardware directly.

It is unclear to me how display(4) interacts with ACPI this way.
On my laptop, the hotkeys generate ACPI-notifications which hotkey
I pressed (display switch or brightness up/down).
Further, to make the actual change happen, the driver must
write back into ACPI - on my laptop at least.

> 
> In this way, no single device has two representations in the device tree
> (think about the consequences, they're not pretty), and every device
> appears in the most appropriate place in the device tree for the purpose
> of suspending, resuming, detaching and re-attaching it.
> 
> Make sense?
> 
> Dave
>