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

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Date:	Thu, 3 Feb 2011 16:30:56 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Airlie <airlied@...il.com>
Cc:	Carlos Mafra <crmafra2@...il.com>,
	Keith Packard <keithp@...thp.com>,
	Dave Airlie <airlied@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Takashi Iwai <tiwai@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Florian Mickler <florian@...kler.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	Linux PM List <linux-pm@...ts.linux-foundation.org>,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	Linux Wireless List <linux-wireless@...r.kernel.org>,
	DRI <dri-devel@...ts.freedesktop.org>
Subject: Re: 2.6.38-rc3-git1: Reported regressions 2.6.36 -> 2.6.37

On Thu, Feb 3, 2011 at 4:06 PM, Dave Airlie <airlied@...il.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
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