From: Keith W. <ke...@tu...> - 2003-04-30 08:36:00
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Benjamin Herrenschmidt wrote: > On Wed, 2003-04-30 at 01:21, Felix Kühling wrote: > >>Benjamin, >> >>I played around with some AGP bits as you suggested in yesterday's IRC >>meeting. I found out that writeback works with 1x and 2x AGP but not >>with 4x. > > > That could mean some clock skew settings should be tweaked... > > As far as I understand AGP, it's a lot of black magic to get it working > regarding the way the host & device are clocked. The radeon's have some > bits to tweak the clock skew for the various speeds, the host bridges > may have more (undocumented) tweaks. The problem is that the HW vendor > binary drivers (both for host and card) do have the workarounds to tweak > those, and we don't... > > In the mean time, a special-case table would be useful to limit known > hosts to some settings we know work... (though that may also depend on > how the given host is configured by the BIOS) I'd prefer to silently fallback to the INREG() solution when the fancy writeback solution looks like it's failing. I guess we could add a blacklist as well, but we shouldn't rely on it. Keith |