Re: sunffb

On Tue, 31 May 2005, Michael wrote:

> We finally got the sunffb driver to work on NetBSD/sparc64, including
> acceleration. Turns out there was a problem in the VIS assembler code:
> 	 wr			%g0, 0, %fprs
> this will turn off the FPU so any subsequent FPU instruction will cause
> a trap. On NetBSD this led to huge numbers of traps which rendered the
> Xserver unusable when acceleration was enabled.
> So for NetBSD I changed this to
> 	 wr			%g0, 4, %fprs
> to leave the FPU active and clean only the dirty bits. No more excessive
> traps and things work.

I'm inclined to simply change both occurrences.

> Since I highly doubt this is an oversight - what's the purpose of
> turning off the FPU after using VIS? Apparently the author expected the
> OS to do something which NetBSD doesn't do, but what? And why? Provoking
> a trap seems a rather expensive way to reset the FPU ( if that's the
> purpose... )

> PS: yes, I mailed the author too

Let us know if you get a response.

Marc.

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