On Tue, 2003-08-12 at 09:49, Egbert Eich wrote:
> Mark Vojkovich writes:
> > NVIDIA root caused this at one point and came to the conclusion
> > that Linux kernel was incorrectly mapping the memory as cached.
> > Experiments with setting bit{63} of Base Register fixed the
> > problem.
> >
>
> OK, this sounds like a very reasonable explanation.
Hmm... It's an interesting observation but I'm a little dubious
because while it may have been true in the past that the Linux
kernel may have failed to map memory as uncached I don't believe
this is true any longer. This assertion has been raised in past with
other ia64 driver bugs and because I'm fortunate enough to sit next to
2 ia64 kernel developers we were able to examine the low level kernel
memory mappings when XFree86 was running and we verified that the MMIO
space was indeed mapped as non-cached. One caveat though, the ia64 kernel
code has been reworked since that exercise so its possible there may
have been a regression. It would be good to verify there has been no
regression, but the kernel engineer who helped is out of the office for
a few days so I'm going to have to wait, but I will post a follow-up.
What did seem to work was to call outb twice rather than once hence
doubling the delay.
What we were seeing here was that the nv driver on HP ZX2000's needed
the outb Egbert added before entering the SlowBCopy loop. But HP ZX6000's
continued to fault. Doubling the outb's seemed to make the ZX6000's
happy. I'm not comfortable with the solution because it feels like
guessing, but it seems to work and I guess that's the bottom line.
John
P.S. this is how the code now looks:
void
xf86SlowBcopy(unsigned char *src, unsigned char *dst, int len)
{
#if defined(__ia64__)
outb(0x80, 0x00);
outb(0x80, 0x00);
#endif
while(len--)
{
*dst++ = *src++;
#if !defined(__sparc__) && !defined(__powerpc__) && !defined(__mips__)
#if defined(__ia64__)
outb(0x80, 0x00);
#endif
outb(0x80, 0x00);
#endif
}
}
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