From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keith Packard <keithp@keithp.com>
Subject: Re: [PATCH] drm/i915: add missing "break"
Date: Mon, 26 Sep 2011 13:56:17 -0700
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To: Chris Wilson <chris@chris-wilson.co.uk>, Paulo Zanoni <przanoni@gmail.com>
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On Fri, 23 Sep 2011 20:07:52 +0100, Chris Wilson <chris@chris-wilson.co.uk>=
 wrote:
> On Fri, 23 Sep 2011 09:15:05 -0700, Keith Packard <keithp@keithp.com> wro=
te:
> > What I didn't find there was any mention of the display_clock_mode
> > field; perhaps jbarnes has newer VBIOS sources or actual BDB
> > documentation.
>=20
> iirc display_clock_mode was found in the Capella VBIOS assembly, so
> indeed comparatively ancient.

Ok, so it appears to have disappeared in more recent hardware. I'm
betting that with PCH hardware, there is always a CK505 source to use,
so the BIOS just uses it unconditionally and may not actually be
configured in the VBT.

> I do enjoy how our best guides for programming the hardware comes from
> RE the bioses. :(

It's not the best, it's just yet another source of information :-)

So, what I think we should be doing is using display_clock_mode to
select between ck505 and internal clock source on pre-PCH hardware. For
PCH hardware, we unconditionally use the ck505 source for the non-SSC
reference. When we need to drive two outputs and are *not* using ck505,
then we disable SSC.

Seem reasonable?

=2D-=20
keith.packard@intel.com

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