linux-kernel - Re: [PATCH] drm/i915: fix failure to power off after hibernate

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Message-ID: <878ufnjfrr.fsf@nemi.mork.no>
Date:	Tue, 24 Feb 2015 20:00:56 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Imre Deak <imre.deak@...el.com>
Cc:	linux-kernel@...r.kernel.org,
	Daniel Vetter <daniel.vetter@...el.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	stable@...r.kernel.org,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: Re: [PATCH] drm/i915: fix failure to power off after hibernate

Imre Deak <imre.deak@...el.com> writes:

> The poweroff handlers undo the actions of the thaw handlers. As the
> original commit stated saving the registers is not needed there, but
> it's also not a big overhead and there should be no problem doing it. We
> are planning to optimize the hibernation sequence by for example not
> shutting down the display between freeze and thaw, and also getting rid
> of unnecessary steps at the power off phase. But before that we want to
> actually unify things rather than having special cases, as maintaining
> the special code paths caused already quite a lot of problems for us so
> far.

That sounds like a worthy goal.  I don't understand what you hope to
achieve by having a poweroff_late hook, since there aren't really
anything useful left to do at the point it is called, but if you want a
dummy callback there for code structure reasons then fine.

But you cannot just run around breaking stuff while slowly moving
towards this goal over multiple releases... v3.19 is currently broken
and that seems totally unnecessary.

In any case: You should have noticed this problem while testing your
patches.  The breakage is 100% reproducible. Unfortunately I had to do a
bisect to realize what you had done to the i915 driver, something I
unfortunately didn't find time to do before v3.19 was released.  But I
do find it unnecessary to release with such bugs.  Any attempt to
exercise the code path you modified would have revealed the bug.

> Reverting the commit may hide some other issue, so before doing that
> could you try the following patch:
> http://lists.freedesktop.org/archives/intel-gfx/2015-February/060529.html

Makes no difference.  I assume that patch fixes an unrelated bug? The
age and reported symptoms indicates so.  Note that I am reporting a
regression introduced after v3.18, while that seems to fix a bug
introduced in v3.17. Both v3.17 and v3.18 (including v3.18.6), as
well as earlier releases, work fine for me.

> If with that you still get the hang could you try on top of that the
> patch below, first having only pci_set_power_state uncommented, then
> both pci_set_power_state and pci_disable_device uncommented?

That patch fixes the problem, with only pci_set_power_state commented
out.  Do you still want me to try with pci_disable_device() commented
out as well?

Bjørn
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