linux-kernel - Re: i915: RC6 causes sudden shutdowns

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Message-ID: <CAGPN=9Q3S0z9aWHyGYPRBfA-iywtJE708v90GDQrpigMVPa-Xg@mail.gmail.com>
Date:	Sat, 3 Dec 2011 16:20:23 +0100
From:	Patrik Kullman <patrik.kullman@...il.com>
To:	Andrew Lutomirski <luto@....edu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: i915: RC6 causes sudden shutdowns

2011/12/3 Patrik Kullman <patrik.kullman@...il.com>:
> 2011/12/2 Andrew Lutomirski <luto@....edu>:
>> On Thu, Dec 1, 2011 at 9:00 PM, Patrik Kullman <patrik.kullman@...il.com> wrote:
>>> 2011/12/1 Andy Lutomirski <luto@....edu>:
>>>> On 11/23/2011 03:43 PM, Patrik Kullman wrote:
>>>>> Hi,
>>>>>
>>>>> I recently acquired the Asus Zenbook UX31E but have been looking for
>>>>> ways to extend the battery life.
>>>>>
>>>>> I read that the i915_enable_rc6 parameter could decrease power usage
>>>>> significantly and tried it with the 3.1.1 and 3.1.2 kernels, and
>>>>> indeed it does.
>>>>> However, I (and the other Zenbook-owners from the Ubuntu forums)
>>>>> experience sudden, unexpected shutdowns (for me, 1-4 times per day)
>>>>> with this parameter.
>>>>> It's as sudden as a power loss.
>>>>
>>>> Do you have DMAR enabled?  If so, it's a known problem and it's being
>>>> worked on (and the default will not change for you AFAICT).  If not, you
>>>> should send a bug report to the intel-gfx -- several people there care
>>>> about this.
>>>>
>>>> --Andy
>>>
>>> Well, it's not something I've explicitly enabled.
>>>
>>> Is it on by default?
>>
>> Depends on config options.  You can probably get a good idea by
>> looking for "DMAR" in your kernel log.
>>
>>>
>>> If so, any reason why I wouldn't want to disable it?
>>
>> There are three reasons to enable it:
>>
>> 1. If you're paranoid and want to (partially) protect your system
>> against malicious PCI/PCIe cards.
>> 2. If you assign devices in your system to VM guests.
>> 3. If you have more than 4GB of RAM and you have DMA-capable devices
>> that can only address 32 bits, then you might get a performance boost.
>>
>> In other words, for normal desktop use, you don't need it.  Try
>> booting with intel_iommu=off.
>>
>> --Andy
>
> As reported by another Ubuntu Zenbook user
> (http://ubuntuforums.org/showpost.php?p=11507684&postcount=207):
>
> Sadly i still get random shutdowns with 3.2-rc4. I have noticed that
> if i just leave my computer on, and does not use it (i have disabled
> the screensaver), the crashes does not accrue.
>
> GRUB_CMDLINE_LINUX_DEFAULT="quiet splash drm.debug=4 intel_iommu=off
> i915.modeset=1 i915.i915_enable_fbc=1 i915.lvds_downclock=1
> i915.i915_enable_rc6=1 pcie_aspm=force"

Something worth mentioning is that the combination of pcie_aspm=force
and intel_iommu=off results in i915.modeset=0, with this combination,
I have to specify i915.modeset=1 to get hardware acceleration.

However, only specifying i915.i915_enable_rc6=1 and intel_iommu=off
keeps modeset=1.

Also I can confirm RC6 and iommu off still causes unexpected
shutdowns, even when booting without FBC, LVDS downclock and
pcie_aspm=force.
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