Re: Multi-seat X crashes

[Helge H. <hel...@ai...>]

Erik Walthinsen wrote:

>Helge Hafting wrote:
>  
>
>>This is probably the classic problem where an xserver mistakenly
>>thinks it has the "only" vga-compatible card in the box, and
>>tries reprogramming video timings using legacy vga hardware
>>addresses that might affect the wrong card.
>>    
>>
>Isn't this what the "VGAAccess" "false" option is for?
>  
>
I don't know, but I'll look at it someday.  I too have this problem,
restarting X on my secondary card messes up the display
on the first, which can be solved by tapping ctrl, alt, and the
big plus on the keypad.  Works for me, but my users get so confused.

Maybe vgaaccess helps.  Maybe using the framebuffer option
will help, according to the docs I'll still get acceleration, but
X will use the framebuffer drivers to do resolution changes.  That
_should_ remove trouble upon x restart, when X tries to set the resolution.

>  
>
>>Third workaround: Configure framebuffers in your kernel,
>>get a framebuffer for each and every screen.
>>    
>>
>This is something I tried for a while, but didn't have much luck with.
>I'll give it another shot though.  Accelleration isn't a huge deal, and
>3D is out with multiple cards anyway, so speed should be acceptible.
>  
>
Actually, 3D isn't out with multiple cards.  I can run 3D both
on my matrox G550 and the radeon 9200 SE at the same time.
It is not _stable_, the kernel will occationally trip up freezing one
or both displays.  So  I don't use it.  But this is merely a bug in
the radeon driver. The kernel, the DRI/DRM 3D systems really support
multihead 3D these days.  My problems is not a result of
dual-seat, running 3D on the radeon alone can go wrong too.

>What I'd really like to be able to do is get both heads of the
>dual-headed cards running separate framebuffers, and get separate X
>servers running on those.  That would let me get away with only 3 video
>cards for 6 heads, freeing other PCI slots for either other cards, or
>smaller motherboards.  Problem is, I couldn't figure out if it is even
>possible to have separate /dev/fb devices with the kernel fb driver...
>  
>
It is possible, but only if the framebuffer driver for that particular
card supports it.  The driver for matrox G550 (and G400)
supports this.  Most other drivers doesn't, so this
really limits your options when buying video cards.
I've done it with the G550 though, when the radeon's
old predecessor died.  I then got the radeon, and got disappointed
with its 3D instability.  So I use it without 3D, mostly because the
G550 seems to dislike 24-bit color which I like. :-/

Matrox also have some cards that really are "two/four cards in one",
in that the pci subsystem believes there are two cards instead of
one.  So they work exactly as two (or four!) cards when setting up
the software. (Kernel framebuffer drivers & xservers.)  But
they don't use up that many slots.  Very expensive though.
Of course a "double" card can justify double price, but they're worse.

>Everything I tried was either 5+ years old and didn't exist anymore, or
>didn't work in the slightest otherwise.
>  
>
Well, matrox works, although old.  And I believe you still can
order the cards too.  "old" shouldn't be a problem if you
consider unaccelerated 2D-only ok though.  (Actually, software
3D rendering works fine with such setups.  Way too slow for a
first-person 3D game of course, but ok for some other
programs like frozen-bubble which isn't really 3D but needs
opengl precence anyway.

Helge Hafting