ATI Drivers report bogus dot_clock to xvidtune

[Egbert Eich]

Alex Deucher writes:
 > 
 > I also don't see how the dotclock would be of any use for vblank, but
 > I suspect you are seeing a limitation of mergedfb.  Mergedfb is
 > basically a hack to treat 2 crtcs as a single screen.  since you have
 > two crtcs with different timings there's no way to know which dotclock
 > or refresh rate, etc. is relevant (since they both are). Hence you end
 > up with some weirdness for certain fields.  Disable mergedfb if you
 > want relevant numbers for those fields.
 > 

I came across a similar problem in randr. It turned out that this really 
ugly hack in radeon_mergefb.c:

     /* Provide a sophisticated fake DotClock in order to trick the vidmode
      * extension to allow selecting among a number of modes whose merged result
      * looks identical but consists of different modes for CRT1 and CRT2
      */
    mode->Clock = (((i->Clock >> 3) + i->HTotal) << 16) | ((j->Clock >> 2) + j->
HTotal);
    mode->Clock ^= ((i->VTotal << 19) | (j->VTotal << 3));


caused the problem. 
I'm not sure if anyone but the author knows what it is good for.
It's not unlikely that the problem with xvidtune is also caused by
this.

Cheers,
	Egbert.