[Nouveau] [Bug 64904] [BISECTED] nouveau, nv50: External VGA not detected anymore

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=64904

--- Comment #12 from Joshua Baergen <joshuabaergen at gmail.com> ---
I can confirm this issue on a ThinkPad W530, NVIDIA Corporation GK107GLM
[Quadro K1000M] (rev a1).  I noticed the issue at work when I tried to connect
to VGA extender which in turn was hooked up to a projector.  However,
connecting directly to a VGA monitor worked fine.

I took Gerhard's suggestion and patched my 2.8.13 Gentoo kernel with the
nv50_dac_detect from ef22c8bb7b3fac45919b7fde412d36d1a8367d51 and I was then
able to connect to the projector.

FWIW, at least one other thing I noticed in the patch is that in the working
code, there's the following sequence:

1) Write (NV50_PDISPLAY_DAC_LOAD_CTRL_ACTIVE | load_pattern) to
DAC_LOAD_CTRL(i).
2) Read DAC_LOAD_CTRL(i).
3) Write 0 to DAC_LOAD_CTRL(i).

In the new code, it's:

1) Write (NV50_PDISPLAY_DAC_LOAD_CTRL_ACTIVE | load_pattern) to
DAC_LOAD_CTRL(i).
2) Write NV50_PDISPLAY_DAC_LOAD_CTRL_DONE to DAC_LOAD_CTRL(i).
3) Read DAC_LOAD_CTRL(i).

Being completely unfamiliar with the hardware, I'm not sure if this is
significant, and unfortunately, I don't have much (if any) opportunity to
experiment.

Josh

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