Multiple screens.

Dave Airlie airlied at
Sat Apr 9 20:33:09 PDT 2005

> Display switching through the bios is disabled by default for mach64
> in current releases. There is a private option to enable it, I believe it is:
> Option "BiosDisplay" "yes"
> However, since my TV-out patch was merged into cvs, bios display
> switching will be on by default for x86, since it is needed for TV-out.
> Note that the TV-out feature as implemented currently and display
> switching through the bios in general is potentially dangerous, since
> it is overriding the normal driver code to set modes (through the card
> registers) with calls to the card bios.  The driver's view of card state
> can become inconsistent with the mode programmed by the bios.
> Although I haven't heard any examples of this causing problems, the
> normal checks of the capabilities of the displays are bypassed.

To be honest I think you might be safer using the BIOS, but then again
I'd say there
are BIOSes out there that do really bad things.. but I think having
TV-OUT support in CVS should outweigh the odd dodgy card... and also
it'll get tested more as we've seen before patches in bugzilla only
get tested by people wanting the feature which doesn't help for those
people who've got a dodgy mach64 with no-TVout but a crap BIOS.. which
hopefully CVS will discover...

> Both for TV-out and clone/dual-head, it would be better to program the
> crtcs directly through the registers as Alex said.  For TV-out, I'm not
> sure if all the relevant information is available to do this on mach64.

We could always use the BIOS to set the registers then read them back
if that is possible, and see if the values have any meaning..


> --
> Leif Delgass
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