Re: [git pull] drm merge for 3.9-rc1

[Linus Torvalds]

On Mon, Feb 25, 2013 at 4:05 PM, Dave Airlie <airlied@xxxxxxxx> wrote:
>
> Highlights:
>
> i915: all over the map, haswell power well enhancements, valleyview macro horrors cleaned up, killing lots of legacy GTT
> code,

Lowlight:

There's something wrong with i915 DP detection or whatever. I get
stuff like this:

[    5.710827] [drm:intel_dp_aux_wait_done] *ERROR* dp aux hw did not
signal timeout (has irq: 1)!
[    5.720810] [drm:intel_dp_aux_wait_done] *ERROR* dp aux hw did not
signal timeout (has irq: 1)!
[    5.730794] [drm:intel_dp_aux_wait_done] *ERROR* dp aux hw did not
signal timeout (has irq: 1)!
[    5.740782] [drm:intel_dp_aux_wait_done] *ERROR* dp aux hw did not
signal timeout (has irq: 1)!
[    5.750775] [drm:intel_dp_aux_wait_done] *ERROR* dp aux hw did not
signal timeout (has irq: 1)!
[    5.750778] [drm:intel_dp_aux_ch] *ERROR* dp_aux_ch not done status
0xa145003f
.....
[    8.149931] [drm:intel_dp_aux_ch] *ERROR* dp_aux_ch not done status
0xa145003f

and after that the screen ends up black.

It's happened twice now, but is not 100% repeatable. It looks like the
message itself is new,  but the black screen is also new and does seem
to happen when I get the message, so...

The second time I touched the power button, and the machine came back.
Apparently the suspend/resume cycle made it all magically work: the
suspend caused the same errors, but then the resume made it all good
again.

Some kind of missed initialization at bootup? It's not reliable enough
to bisect, but I obviously suspect commit 9ee32fea5fe8 ("drm/i915:
irq-drive the dp aux communication") since that is where the message
was added..

Btw, looking at that commit, what do you think the semantics of the
timeout in something like

    done = wait_event_timeout(dev_priv->gmbus_wait_queue, C, 10);

would be? What's that magic "10"? It's some totally random number.

Guys, it should be something meaningful. If you meant a tenth of a
second, use HZ/10 or something. Because just the plain "10" is crazy.
I happen to have CONFIG_HZ_1000=y, and you're apparently waiting for a
hundreth of a second. Was that what you intended? Because if it was,
it is still crap, since CONFIG_HZ might be 100, and then you're
waiting for ten times longer.

IOW, passing in a random number like that is crazy. It cannot possibly
be right.

I have no idea whether the timeout has anything to do with anything,
but it reinforces my suspicion that there is something wrong with that
commit.

                   Linus
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