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

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Message-ID: <87bnkhqan8.fsf@nemi.mork.no>
Date:	Thu, 26 Feb 2015 10:34:19 +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:

>> 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?
>
> No, but it would help if you could still try the two attached patch
> separately, without any of the previous workarounds. Based on the
> result, we'll follow up with a fix that adds for your specific platform
> either of the attached workarounds or simply avoids putting the device
> into D3 (corresponding to the patch you already tried).

None of those patches made any difference.  The laptop still hangs at
power-off.

Not really surprising, is it?  Previous testing shows that the hang
occurs at the pci_set_power_state(drm_dev->pdev, PCI_D3hot) call in the
poweroff_late hook.  It is hard to see how replacing it by an attempt to
set D3cold, or adding any call after this point, could possibly change
anything.  The system is stil hanging at the pci_set_power_state() call.

The generic pci-driver code will put the i915 device into PCI_D3hot for
you, won't it?  Why do you need to duplicate that in the driver,
*knowing* that doing so breaks (at least some) systems?

I honestly don't think this "let's try some random code" is the proper
way to fix this bug (or any other bug for that matter).  You need to
start understanding the code you write, and the first step is by
actually explaining the changes you make.

I also believe that you completely miss the fact that this bug has
survived a full release cycle before you became aware of it, and the
implications this has wrt other affected systems/users.  I assume you
understand that my system isn't one-of-a-kind, This means that there are
other affected users with identical/similar systems.  Now, if none of
those users reported the bug to you (we all know why: Linux kernel
development is currently limited by the available testing resources, NOT
by the available developer resources), then how do you know that there
aren't a number of other systems affected as well?

Let me answer that for you:  You don't.

Which is why you must explain the mechanism triggering the bug, proving
that it is a chipset/system specific issue.  Because that's the only way
you will *know* that you have solved the problem not only for me, but for
all affected users.

IMHO, the only safe and sane solution at the moment is the revert patch
I posted.  It's a simple fix, reverting back to the *known* working
state before this regression was introduced.

Then you can start over from there, trying to implement this properly.

Thanks,
Bjørn
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