Re: matroxfb-fix-dvi-setup-to-be-more-compatible.patch introduces jitter

Re: matroxfb-fix-dvi-setup-to-be-more-compatible.patch introduces jitter

[Paul A. Clarke]

I've been looking deeper into this problem, which was reportedly introduced by 
my patch a while ago, in Linux kernel 2.6.17.  I don't doubt the reports, but 
I'd like to replicate the problem as seen on the x86 boxes as reported in kernel 
bug 6720 and a few others directly to me, so I can verify a fix (if/when I can 
create one).

So, I installed SLES 10 on an old x86 box, with a PCI G450 (actually an IBM 
GXT135P).  I verified that my patch is _not_ included in that kernel 
(2.6.16.21).  However, I see jittery DVI-D output at all times.  I've tried 
640x480@60Hz, 1280x1024@60Hz, different "vesa" mode parameters (0x11b, 0x1bb), 
XServer "-fbbpp 32".  I usually end up losing sync with the monitor after a few 
minutes.

I don't have much experience with the G450 on x86, but I'm quite surprised.  Has 
anyone else observed this?
-- 
Regards,
Paul Clarke

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Re: matroxfb-fix-dvi-setup-to-be-more-compatible.patch introduces jitter

[Petr Vandrovec]

Paul A. Clarke wrote:
> I've been looking deeper into this problem, which was reportedly 
> introduced by my patch a while ago, in Linux kernel 2.6.17.  I don't 
> doubt the reports, but I'd like to replicate the problem as seen on the 
> x86 boxes as reported in kernel bug 6720 and a few others directly to 
> me, so I can verify a fix (if/when I can create one).
> 
> So, I installed SLES 10 on an old x86 box, with a PCI G450 (actually an 
> IBM GXT135P).  I verified that my patch is _not_ included in that kernel 
> (2.6.16.21).  However, I see jittery DVI-D output at all times.  I've 
> tried 640x480@60Hz, 1280x1024@60Hz, different "vesa" mode parameters 
> (0x11b, 0x1bb), XServer "-fbbpp 32".  I usually end up losing sync with 
> the monitor after a few minutes.
> 
> I don't have much experience with the G450 on x86, but I'm quite 
> surprised.  Has anyone else observed this?

I believe that problem is not x86 vs. ppc, but type of monitor you have 
connected to the box.

Perhaps try walkdvi 
(http://platan.vc.cvut.cz/ftp/pub/linux/matrox-latest/walkdvi.tar.gz, it will 
probably need some fixes for big endian) with different XDVICLKCTL values.  Code 
to set XPANMODE (in g450_set_plls) was written based on experimenting with 
couple of devices I had, so maybe right thing is not modifying XDVICLKCTL 
register, but instead teaching PLL code to try different XPANMODE values if PLL 
does not lock in reasonable time.
								Petr


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