[Bug 17902] [830M missing dvo driver] need support for DVO-LVDS via na2501

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=17902

--- Comment #78 from Daniel Vetter <daniel at ffwll.ch> 2012-05-29 14:13:48 PDT ---
> --- Comment #77 from thor at math.tu-berlin.de 2012-05-29 14:05:28 PDT ---
> Sorry if this sounds like a stupid question - but how come that i2cdetect only
> sees one bus when booting with the vga frame buffer, but 7 with the i915drm
> module in place? Is there anything I need to do to activate the remaining
> busses (not devices! - that will be the next problem - it is also a problem
> that bus #6 does not always lists the ns2501).

We expose all the i2c lines that the gpu can drive as normal i2c
buses. Some are used to read the edid from vga connected screens,
others to communicate to dvo chips. Dunno why ns2501 doesn't show up
all the time for you.

> A second remark is that I found that the documentation I have on the ns2501
> does not include the registers for the scaler (*sigh*), so that's my fault.
> I'll see what I can find.

The scaler is on the gpu side. See the funky computations in
intel_lvds_mode_ fixup in intel_lvds.c and all the pfit_ values
computed in there (grep for these to get to the code that uses them).

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