Messages in this thread | | | Date | Sun, 18 May 2003 23:34:46 +0100 | From | Jamie Lokier <> | Subject | Re: [PATCH] Use MTRRs by default for vesafb on x86-64 |
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Alan Cox wrote: > > What exactly "doesn't work" with these cards? > > If you sent an MTRR you get crap on the display. I'm not sure if that is > registers being covered (seems dubious) or other PCI problems perhaps > with bursts
Is it consistently bad, or is it just an occasional glitch, pixel here or there that goes wrong?
I like your suggestion of PCI bursts - perhaps the card's FIFO to video RAM overflows due to RAM being too slow or too busy for display reads. It seems quite plausible. It might even depend on the video mode.
If that's the problem, a test which writes a data pattern to a significant chunk of video RAM in sequence, as fast as possible, and then reads it would be practically guaranteed to spot this and indicate that MTRRs aren't suitable for this card in this mode.
-- Jamie
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