To implement a PPGTT for drm/i915 that fully aliases the GTT, we also
need to properly alias the scratch page.
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Chris Wilson and me have again stared at funny error states and it's
been pretty clear from the start that something was seriously amiss.
The seqnos last seen by the cpu were a few hundred behind those that
the gpu could have possibly emitted last before it died ...
Chris now tracked it down (hopefully, definit verdict's still out),
but in hindsight we'd have found the bug by simply dumping the cpu
side tracking of the ring head and tail registers.
Fix this and prevent an identical time-waster in the future.
Because the hangs always involved semaphores in one way or another,
we've tried to dump the mbox registers, but couldn't find any
inconsistencies. Still, dump them too.
Reviewed-and-wanted-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
These are all user-trigerable, so tune down their loudness a notch.
For some of these we have i-g-t tests (because they prevent
newly-discovered bugs), without this patches running the test suite
leaves behind a dirty dmesg.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
On gen5 we also need to correctly set up swizzling in the display
scanout engine, but only there. Consolidate this into the same
function.
This has a small effect on ums setups - the kernel now also sets this
bit in addition to userspace setting it. Given that this code only
runs when userspace either can't (resume, gpu reset) or explicitly
won't(gem_init) touch the hw this shouldn't have an adverse effect.
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
We have to do this manually. Somebody had a Great Idea.
I've measured speed-ups just a few percent above the noise level
(below 5% for the best case), but no slowdows. Chris Wilson measured
quite a bit more (10-20% above the usual snb variance) on a more
recent and better tuned version of sna, but also recorded a few
slow-downs on benchmarks know for uglier amounts of snb-induced
variance.
v2: Incorporate Ben Widawsky's preliminary review comments and
elaborate a bit about the performance impact in the changelog.
v3: Add a comment as to why we don't need to check the 3rd memory
channel.
v4: Fixup whitespace.
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
As the buffer is not necessarily accessible through the GTT at the time
of a GPU hang, and capturing some of its contents is far more valuable
than skipping it, provide a clflushed fallback read path. We still
prefer to read through the GTT as that is more consistent with the GPU
access of the same buffer. So example it will demonstrate any errorneous
tiling or swizzling of the command buffer as seen by the GPU.
This becomes necessary with use of CPU relocations and lazy GTT binding,
but could potentially happen anyway as a result of a pathological error.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Like for shmem_pwrite_slow. The only difference is that because we
read data, we can leave the fetched cachelines in the cpu: In the case
that the object isn't in the cpu read domain anymore, the clflush for
the next cpu read domain invalidation will simply drop these
cachelines.
slow_shmem_bit17_copy is now ununsed, so kill it.
With this patch tests/gem_mmap_gtt now actually works.
v2: add __ to copy_to_user_swizzled as suggested by Chris Wilson.
v3: Fixup the swizzling logic, it swizzled the wrong pages.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38115
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
... instead of get_user_pages, because that fails on non page-backed
user addresses like e.g. a gtt mapping of a bo.
To get there essentially copy the vfs read path into pagecache. We
can't call that right away because we have to take care of bit17
swizzling. To not deadlock with our own pagefault handler we need
to completely drop struct_mutex, reducing the atomicty-guarantees
of our userspace abi. Implications for racing with other gem ioctl:
- execbuf, pwrite, pread: Due to -EFAULT fallback to slow paths there's
already the risk of the pwrite call not being atomic, no degration.
- read/write access to mmaps: already fully racy, no degration.
- set_tiling: Calling set_tiling while reading/writing is already
pretty much undefined, now it just got a bit worse. set_tiling is
only called by libdrm on unused/new bos, so no problem.
- set_domain: When changing to the gtt domain while copying (without any
read/write access, e.g. for synchronization), we might leave unflushed
data in the cpu caches. The clflush_object at the end of pwrite_slow
takes care of this problem.
- truncating of purgeable objects: the shmem_read_mapping_page call could
reinstate backing storage for truncated objects. The check at the end
of pwrite_slow takes care of this.
v2:
- add missing intel_gtt_chipset_flush
- add __ to copy_from_user_swizzled as suggest by Chris Wilson.
v3: Fixup bit17 swizzling, it swizzled the wrong pages.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
The gtt_pwrite slowpath grabs the userspace memory with
get_user_pages. This will not work for non-page backed memory, like a
gtt mmapped gem object. Hence fall throuh to the shmem paths if we hit
-EFAULT in the gtt paths.
Now the shmem paths have exactly the same problem, but this way we
only need to rearrange the code in one write path.
v2: v1 accidentaly falls back to shmem pwrite for phys objects. Fixed.
v3: Make the codeflow around phys_pwrite cleara as suggested by Chris
Wilson.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This will also come handy for the gen6+ swizzling support, where the
driver is supposed to control swizzling depending upon dram
configuration.
v2: CxDRB3 are 16 bit regs! Noticed by Chris Wilson.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
It looks like the desktop variants of i915 and i945 also have the DCC
register to control dram channel interleave and cpu side bit6
swizzling.
Unfortunately internal Cspec/ConfigDB documentation for these ancient chips
have already been dropped and there seem to be no archives. Also
somebody thought the swizzling behaviour is surely a worthy secret to
keep and redacted any mention of these fields from the published Intel
datasheets.
I suspect the hw engineers were really proud of the page coloring
they've achieved in their first dual channel dram controller with
bit17 - after all Bspec explains in great length the optimal layout of
page frame numbers modulo 4 for the color and depth buffers, too.
Later on when they've started to work on VT-d they shamefully
discoverd their stupidity and tried to cover the tracks ...
Tested-by: Daniel Vetter <daniel.vetter@ffwll.ch> (i915g)
Tested-by: Pavel Ondračka <pavel.ondracka@email.cz> (i945g)
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=42625
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
The original intention of comparing the bo against the mappable GTT
limits was to prevent a subsequent faulting of the bo into the GTT from
clearing the entire GTT in vain. However, that was clearly a cut'n'paste
mistake as a CPU mapping never binds the bo into the aperture. Whilst
there may be some merit to limiting the maximum size of the bo to
something that can be utilized by the GPU, that limit itself does not
belong as a safeguard to mmapping the bo, so remove the check entirely.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This was pretty handy when figuring out what exactly went wrong with
ppgtt and it might also be useful when we stop filling the entire gart
with scratch page entries.
Also add the gen6+ DONE reg while at it.
v2: Chris Wilson suggested to allocate the error_state with kzalloc
for better paranoia. Also kill existing spurious clears of the
error_state while at it.
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This confuses our domain tracking and can (for gtt write domains) lead
to a subsequent oops.
Tested by tests/gem_exec_bad_domains from i-g-t.
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
With the error_state facility in place, this has outlived it's
usefulness. It also oopses with the lates llc-reloc patches because
it directly access objects through the gtt without any checks.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Since quite a while we also the basic output configuration in the
error_state, so it should contain enough information to diagnose
these MI_WAIT hangs.
Reviewed-and-tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
All r/w debugfs files are created equal.
v2: Add some newlines to make the code easier on the eyes as requested
by Ben Widawsky.
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Only forcewake has an open with special semantics, the other r/w
debugfs only assign the file private pointer.
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
With the fence accounting fixed up in the previous commit not finding
enough fences is a fatal error and userspace bug. Trashing the entire
gtt is not gonna turn up that missing fence, so don't to this by
returning another error thatn ENOSPC.
This has the added benefit that it's easier to distinguish fence
accounting errors from gtt space accounting issues.
TTM serves as precendence for the EDEADLK error code - it returns it
when the reservation code needs resources already blocked by the
current reservation.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
In order to correctly account for reserving space in the GTT and fences
for a batch buffer, we need to independently track whether the fence is
pinned due to a fenced GPU access in the batch or whether the buffer is
pinned in the aperture. Currently we count the fenced as pinned if the
buffer has already been seen in the execbuffer. This leads to a false
accounting of available fence registers, causing frequent mass evictions.
Worse, if coupled with the change to make i915_gem_object_get_fence()
report EDADLK upon fence starvation, the batchbuffer can fail with only
one fence required...
Fixes intel-gpu-tools/tests/gem_fenced_exec_thrash
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38735
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: Paul Neumann <paul104x@yahoo.de>
[danvet: Resolve the functional conflict with Jesse Barnes sprite
patches, acked by Chris Wilson on irc.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This was just to facilitate product enablement with pre-production hw.
Allows us to kill quite a bit of cruft.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Based on a patch by Ben Widawsky, but with different colors
for the bikeshed.
In contrast to Ben's patch this one doesn't add the fault regs.
Afaics they're for the optional page fault support which
- we're not enabling
- and which seems to be unsupported by the hw team. Recent bspec
lacks tons of information about this that the public docs released
half a year back still contain.
Also dump ring HEAD/TAIL registers - I've recently seen a few
error_state where just guessing these is not good enough.
v2: Also dump INSTPM for every ring.
v3: Fix a few really silly goof-ups spotted by Chris Wilson.
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
The code already got unwieldy and we want to dump more per-ring
registers.
Only functional change is that we now also capture the video
ring registers on ilk.
v2: fixup a refactor fumble spotted by Chris Wilson.
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
... and add a helpr function for the places where we want a flag.
This way we can use ring->id to index into arrays.
v2: Resurrect the missing beautification-space Chris Wilson noted.
I'm moving this space around because I'll reuse ring_str in the next
patch.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
It should be programmed to "0" for HDMI or "1" for DisplayPort.
This enables DisplayPort audio for
- HP EliteBook 8460p
(whose BIOS does not set the N_value_index bit for us)
- DisplayPort monitor hot plugged after boot
(otherwise most BIOS will fill the N_value_index bit for us)
Tested-by: Robert Lemaire <rlemaire@suse.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This is only relevant when using module unloading, and really only helps
get rid of a probably benign warning.
I can't remember if I sent this out already, but it's not turning up in
any of my searches.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
After the ILK vt-d workaround patches it became clear that we had
introduced a bug. Chris Wilson tracked down the issue to recursive
calls to unmap. This happens because we try to optimize waiting on
requests by calling retire requests after the wait, which may drop the
last reference on an object and end up freeing the object (and then
unmap the object from the gtt).
After the last patch we can now choose to defer processing the retire
list.
Kudos to Chris Wilson for tracking this one down.
This patch fixes gem_unref_active_buffers from i-g-t. It was tested by
forcing do_idle_maps to true.
This also fixes tests/gem_linear_blits in intel-gpu-tools.
Reported-by: guang.a.yang@intel.com
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=42180
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Sometimes it may be the case when we idle the gpu or wait on something
we don't actually want to process the retiring list. This patch allows
callers to choose the behavior.
Reviewed-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Older specs claimed this was bit 11, but newer specs and the actual
simulator code say it was bit 12. Regardless, we don't use MI_FLUSH,
or try to enable it any more.
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: Anyone trying to use this bit, please read all the relevant
discussions, it's epic.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
We have always been using the wrong bit -- it's bit 12. However, the
bit also doesn't do anything -- hardware has always accepted the
MI_FLUSH command even when it was specced not to.
Given that there is only one MI_FLUSH emitted in all of the driver
stack on gen6+ (in i965_video.c of the 2d driver, and it should be
using other code to do its flush instead), just remove the MI_FLUSH
enable instead of trying to fix it.
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This was completely spamming dmesg on my i855gm. This issue was just
shortly introduced with:
commit 931872fcea
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon Jan 16 23:01:13 2012 +0000
drm/i915: Check that plane/pipe is disabled before removing the fb
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Otherwise, we are left with pretty bogus message saying that the pixel
format is not supported while leaving the details to the telepatic powers.
v2: use DRM_DEBUG_KMS instead of DRM_ERROR
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Now that we're using the sprite WM fields, we need to take care not to
clobber them in the main update_wm functions. While we're at it, make
sure we mask out the old sprite wm value before or'ing in the new one
when the sprite wm is updated.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
I've reviewed gen2 pageflip code to hunt down multiple prepare pageflip
issues. The only thing I've found is a slight but functionally
meaningless confusion about the length of the mi cmd.
Fix it up and add a comment about what this dword should be (according
to docs at least).
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
LLC is not SNB/IVB-specific, so we should check for it in a more generic
way.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Some decent history digging indicates that this was to be used for the
GLX_MESA_allocate_memory extension but never actually implemented for
any released i915 userspace code.
So just rip it out.
v2: Fixup the Makefile.
Acked-by: Dave Airlie <airlied@gmail.com>
Cc: Keith Whitwell <keithw@vmware.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
The advantage of kcalloc is, that will prevent integer overflows which could
result from the multiplication of number of elements and size and it is also
a bit nicer to read.
The semantic patch that makes this change is available
in https://lkml.org/lkml/2011/11/25/107
Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This is paranoid, but I am entirely willing to believe the hardware
could come up with a condition where I get a status with both the 'done'
and 'receive error' bits set.
Signed-off-by: Adam Jackson <ajax@redhat.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
The default in the Sandybridge docs is 5, as on Ironlake, and I have no
reason to believe 3 would work any better.
Signed-off-by: Adam Jackson <ajax@redhat.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Matches the advice in the Sandybridge documentation.
Signed-off-by: Adam Jackson <ajax@redhat.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
There is an error in i915_read_blc_pwm_ctl, where the register values
are not being copied correctly. BLC_PWM_CTL and BLC_PWM_CTL2 are
getting mixed up. This patch fixes that so that saveBLC_PWM_CTL2 and
not saveBLC_PWM_CTL is copied to the BLC_PWM_CTL2 register.
Signed-off-by: Simon Que <sque@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Staring at an error state such as:
PGTBL_ER: 0x00000400
Display B: Invalid tiling
fence[0] = 05001001
valid, x-tiled, pitch: 512, start: 0x05000000, size: 1048576
Pinned [2]:
00000000 131072 0001 0001 00000000 P uncached
00020000 4096000 0041 0000 00000000 P uncached (name: 1)
Plane [1]:
CNTR: c0000000 # enabled | gamma
STRIDE: 00001400
SIZE: 03ff04ff
POS: 00000000
ADDR: 05000000
Suggests that we did not clear the DSPBCNTR prior to unpinning the
framebuffer and reusing the GTT space. Impossible! Unless our DPMS
bookkeeping ran afoul again...
In the meantime add an assertion that the plane is decoupled from the
framebuffer prior to release.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Fix function name in comments, a left-over from when i965_reset was
renamed to i915_reset.
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This cleans up the mode set path a little further, making it easier to
extend for future platforms.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: shut up stupid gcc warning about potential use of
un-initlized fp2]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Makes the mode set routine a little cleaner and easier to extend.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This is needed to run the simulator.
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: added a comment in case people wonder what it's for.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
