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Date:	Sat, 3 Dec 2011 09:19:29 +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

2011/12/2 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"
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