[Bug 48880] Set mode has different timings than requested on VGA

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=48880

--- Comment #21 from Alex Deucher <agd5f at yahoo.com> 2012-04-19 07:20:44 PDT ---
(In reply to comment #20)
> What about the BIOS bug angle? Because kernel is not setting up the hardware
> directly, but asking the BIOS to do it, right? Is that out of the question?

It's not out of the question, but I highly doubt it.  The driver calculates the
pll dividers and the atom table basically writes them to the pll registers.  If
there was a bug in the table, I'd expect it to cause problems across the board,
not just on one mode on one monitor.  We've had lots of these kind of bugs over
the course of the driver's life.  Some combinations of dividers and monitors
are just not happy.  The trick is to tweak the algo just enough to fix the
problematic monitor while not breaking others.  I'll test
RADEON_PLL_USE_FRAC_FB_DIV on the hw I have here and if all goes well, I'll
send it to Dave.

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