[Intel-gfx] Meaning of "fbpercrtc=1" option?
tobias.hain at gmx.de
Wed Oct 7 10:14:37 CEST 2009
I'm using KMS on the latest ubuntu 9.10 bits. My notebook 1280 x 800 is docked
to an external 1920 x 1200 display.
I'm facing two inconvenieces:
i) During boot both the internal LVDS and external DVI display show the same
console content. It's a clone,where only the upper left part of the bigger
1920 x 1200 display is used for 1280 x 800 output. Much space of the external
display is unusable
ii) Once X has fired up and I can switch with KMS Crtl + Alt + Fn between the
console and X. The console still only uses a fraction of the bigger display,
but switching works fine. However the console output on the LVDS internal
display doesn't turn OFF once switched to X again. That means: While the
external display shows X, the LVDS shows a stalled console session (backlight
I resolved both issues by booting with "fbpercrtc=1" option, which I found in
the source code. It boots fine with a huge 1920 x 1200 console only on the
external screen and switching between X and console leaves the internal LVDS
turned off. That's the way I want to use it.
However I don't know what this option actually does:
. Is it safe to use? Or less/untested code?
. Does it consume more memory - maybe because it allocates memory for two
framebuffer consoles? Is there an option to e.g. force enabling just one fb -
the bigger one?
. Can the LVDS and DVI framebuffer console used indepenently? dmesg shows me
It's not directly related, but the intel X driver uses
(II) intel(0): Using fuzzy aspect match for initial modes
whose meaning keith described in his blog. I would like to see an override for
this one in xorg.conf. Nobody else?
For both KMS fb console and X initial mode I'd like to tell my system: Use the
biggest display only.
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