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SUMMARY: On the ASUS UX21E ultrabook, enabling SNA graphics acceleration
leads to spontaneous shutdowns while watching Flash video in full screen
AND using the battery as the power source, the problem starts surfacing
once the battery charge level drops below 33%. The issue affects both
x86 and x64 platforms, affects at least the 14.04 and 14.10 Ubuntu
versions, affects at least the regular Ubuntu and its Kubuntu and
Lubuntu flavors, affects at least kernels 3.13, 3.14, 3.15, 3.16, 3.17,
3.18, 3.19 and 4.0. The issue can't be fixed by changing the various
i915 driver options like rc6 and semaphores, neither does PCIE_ASPM play
a role. Repetitive triggering of the bug runs the machine into an even
weirder state where it would chaotically reboot every time a higher-
than-moderate strain is put on the GPU, and the only way to fix this is
to detach both battery connectors from the motherboard for a while (CMOS
battery and the main power source battery) The issue surprisingly
disappears after a hard CMOS reset AND setting the acceleration method
to UXA. The BIOS version of my UX21E is 214.  I've also taken my UX21 to
the official ASUS service center and after running the tests they
replied that the unit has no hardware issues, so it is a Linux issue. A
vaguely similar issue is reported to affect UX21E running Windows 8, so
it may be a crippled DSDT after all.

THE LONG STORY:

=========================================================================================

IMPORTANT UPDATE! As of 14.04 and 14.10 using the default SNA graphics
acceleration instead of UXA leads to unexpected shutdowns and/or CMOS
settings corruption. To activate the bug, one must be:

-- Using the battery as the power source

-- Having the battery charge below 33%

-- Watching a FULLSCREEN video in Flash Player (e.g. youtube)

-- Both Pepper Flash in Chrome/Chromium and the regular Adobe Flash in
Firefox/Chromium are affected

This is the most typical scenario for triggering an unexpected shutdown,
but other variants do exist. Certain Flash-heavy sites like
speedtest.net can trigger this, as well as KDE's KWin window compositor
with certain GLX-accelerated eye candy options turned on. The bug also
affects at least Kubuntu and Lubuntu, but that's just what I was able to
confirm. Most likely it affects all other Ubuntu flavors and even other
distributions that use the latest Intel video drivers AND employ SNA as
the default acceleration method.

The issue persists with various Ubuntu versions (at least 14.04 &
14.10), various kernel versions (I tried almost every kernel from 3.13
to 4.0) and even using the cutting-edge drivers from the xorg-edgers PPA
does nothing to fix this. Both x86 and x64 platforms are affected. Flash
Player version plays no role, either. The bug apparently happens because
the ultrabook's ACPI-based power management mechanisms just can't get on
terms with the latest implementation of SNA. Something happens when the
battery charge drops below 1/3 -- and once SNA draws too much power from
the GPU, a shutdown happens. The various i915.* driver options like rc6
and semaphores do nothing to fix this!

The worst thing is that after you get several unexpected shutdowns, your
UX21E may start rebooting chaotically whenever any program tries to use
graphics acceleration, be it Chromium's accelerated canvas rendering or
simply the window manager using transparency. This further leads to file
system corruption up to the point when you can no longer boot into your
user profile. You can still create another user profile via the
terminal, but this does not get rid of the reboot glitch.

If you happen to run into this, you must perform a hard CMOS reset. To
do this, one must unscrew the twelve torx screws and remove the bottom
part of the casing, then detach *BOTH* the main battery connector and
the CMOS battery connector from the motherboard, then wait for a few
minutes and attach them back. Flushing CMOS programmatically with a
command-line utility like CmosPwd does not fix this issue! If you are
unsure how to open your UX21E or detach the battery connectors, search
youtube for an UX21E disassemby guide -- detaching the battery on this
model used to be a popular trick a few years ago when a certain Windows
glitch caused similar behavior and required hard CMOS reset as well, so
there are a number of videos and forum threads on this issue across the
web.

Once you have made sure your CMOS is okay (that is, you don't get
frequent shutdowns shortly after logging into the system while working
on battery with a charge below 33%) you can proceed to fix the ultimate
cause of this issue. If it exists, delete the
/usr/share/X11/xorg.conf.d/20-intel.conf file then create a new one
containing the following lines:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Section "Device"

Identifier "Intel Graphics"

Driver "intel"

Option "AccelMethod" "uxa"

EndSection

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Reboot and the issue is fixed!

I also recommend using the following kernel boot arguments with this
model to provide maximum power saving and stability in 14.04 and 14.10:

intel_pstate=enable pcie_aspm=force pcie_aspm.policy=default
ath9k.ps_enable=1 i915.semaphores=1 i915.enable_rc6=7 i915.powersave=1
i915.lvds_downclock=1 drm.vblankoffdelay=1 i915.enable_fbc=1

Enabling 'i915.enable_fbc' and 'i915.lvds_downclock' can lead to minor
graphical glitches with SNA acceleration, but since SNA is a no go due
to the above mentioned bug, you can safely turn them on with UXA.
'pcie_aspm' absolutely needs being set to 'force' and 'pcie_aspm.policy'
to 'default' -- the UX21E is very picky about this as of the latest
official kernels in 14.04 and 14.10. 'ath9k.ps_enable' is required to
enable wireless power saving in power managing software like TLP

I hope someone re-formats my remarks to fit into the article in a more
befitting manner and/or files a bug on the Ubuntu bug tracker because
I'm almost exhausted and broken while typing this. Tracking this sucker
down cost me almost two months of my life because once you run into the
chaotic reboot issue, you can't fix anything without hard resetting the
CMOS, and it took me too long to realize.

Thanks for understanding.

P.S. This may also affect other Asus ultrabooks with integrated Intel
graphics like UX31E. A Windows bug with very similar symptoms is known
to affect the whole model line, especially with Windows 8.1

=========================================================================================

** Affects: xorg (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: bot-comment
-- 
SNA acceleration causes sudden shutdowns and corrupts CMOS data on the the Asus UX21E ultrabook on a wide variety of kernels since at least Ubuntu 14.04
https://bugs.launchpad.net/bugs/1446027
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