Display specification

Adam Jackson ajax at nwnk.net
Mon Mar 14 10:44:09 PST 2005


On Monday 14 March 2005 13:09, Jon Smirl wrote:
> Doing something like this:
> EGLDisplay dpy = eglGetDisplayForWidgetXXX("pci/0000:01:00.0");
> builds a dependence in on card location. you don't want to do that.
> <snip>
> The basic idea is that the kernel knows about physical devices. It
> then finds and loads the appropriate device driver. The driver then
> exposes user space accessible /sys/class entries. All of the device
> discovery process is removed from XGL/X.

I'm not seeing how this makes /sys/class/graphics/fb0 independent of card 
location, unless you set up those bindings by calling out to userspace.  I'm 
not insistent on being able to specify a display by bus address.  However I 
do want a deterministic way to pick a specific card independent of the 
kernel's probe order.  If that means asking for "screen/0" which is defined 
by some config file somewhere to be "the Voodoo3 as opposed to the G400", 
fine.

I think the idea of not needing a config file is very noble, but in practice 
it's just not going to happen for multiseat.  You cannot uniquely identify 
most HID devices by anything other than bus location, because HID devices are 
dumb and lack unique serial numbers.  You can manage this config file 
dynamically and call it a policy agent if it makes you feel better, but it's 
still userspace configuration.

Also there exist less fortunate OSes where we don't have sysfs, so we may need 
the ability to specify devices by bus address anyway.

- ajax
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