Re: 2.6.38-rc3-git1: Reported regressions 2.6.36 -> 2.6.37

Linus Torvalds
2011-02-04T00:30:56Z

On Thu, Feb 3, 2011 at 4:06 PM, Dave Airlie <airlied@gmail.com> wrote:
>
> If we are setting a mode on a connector it automatically will end up
> in a DPMS on state,
> so this seemed correct from what I can see.

The more I look at that function, the more I disagree with you and
with that patch.

The code is just crazy.

First off, it isn't even necessarily setting a mode to begin with,
because as far as I can tell. If the mode doesn't change, neither
mode_changed nor fb_changed will be true, afaik. There seems to be a
fair amount of code there explicitly to avoid changing modes if not
necessary.

But even _if_ we are setting a mode, if I read the code correctly, the
mode may be set to NULL - which seems to mean "turn it off". In which
case it looks to me that drm_helper_disable_unused_functions() will
actually do a

(*crtc_funcs->dpms)(crtc, DRM_MODE_DPMS_OFF);

call on the crtc in question. So then blindly just saying "it's mode
DRM_MODE_DPMS_ON" afterwards looks rather bogus to me.

_Maybe_ it would work if it was done before that whole
"disable_unused" logic. Or maybe it should just be done in
drm_crtc_helper_set_mode(), which is what actually sets the mode (but
there's the 'fb_changed' case too)

> A future mode set shouldn't ever not turn the connector on, since
> modesetting is an implicit
> DPMS,
>
> It sounds like something more subtle than that, though I'm happy to
> revert this for now, and let Keith
> think about it a bit more.

So I haven't heard anything from Keith. Keith? Just revert it? Or do
you have a patch for people to try?

Linus