Exercising the gpu reloc path strenuously revealed an issue where the
updated relocations (from MI_STORE_DWORD_IMM) were not being observed
upon execution. After some experiments with adding pipecontrols (a lot
of pipecontrols (32) as gen4/5 do not have a bit to wait on earlier pipe
controls or even the current on), it was discovered that we merely
needed to delay the EMIT_INVALIDATE by several flushes. It is important
to note that it is the EMIT_INVALIDATE as opposed to the EMIT_FLUSH that
needs the delay as opposed to what one might first expect -- that the
delay is required for the TLB invalidation to take effect (one presumes
to purge any CS buffers) as opposed to a delay after flushing to ensure
the writes have landed before triggering invalidation.
Testcase: igt/gem_tiled_fence_blits
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181105094305.5767-1-chris@chris-wilson.co.uk
Older gen use a physical address for the hardware status page, for which
we use cache-coherent writes. As the writes are into the cpu cache, we use
a normal WB mapped page to read the HWS, used for our seqno tracking.
Anecdotally, I observed lost breadcrumbs writes into the HWS on i965gm,
which so far have not reoccurred with this patch. How reliable that
evidence is remains to be seen.
v2: Explicitly pass the expected physical address to the hw
v3: Also remember the wild writes we once had for HWS above 4G.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180903152304.31589-2-chris@chris-wilson.co.uk
This reapplies commit 39f3be162c ("drm/i915: Kick waiters on resetting
legacy rings") after the improved gem_eio was run across all machines we
found that gen3 and early gen4 still lost the immediate interrupt
following reset, and the HWSTAM w/a applied to gen6+ is inadequate.
Unlike the later gen, on gen3/4 the principle (and only tests to fail so
far) are the wait vs reset test cases, whereas the reset stress case
works fine (which was the predominantly failing case for gen6+). That is
enough to suggest the underlying issue is sufficiently different to
support the difference in HWSTAM efficacy.
Testcase: igt/gem_eio/wait-10ms
References: 39f3be162c ("drm/i915: Kick waiters on resetting legacy rings")
References: a69ab52b03 ("drm/i915: Remove extra waiter kick on legacy resets")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180814104056.27001-1-chris@chris-wilson.co.uk
After disabling resource streamer on ICL (due to it actually not
existing there), I got feedback that there have been some experimental
patches for mesa to use RS years ago, but nothing ever landed or shipped
because there was no performance improvement.
This removes it from kernel keeping the uapi defines around for
compatibility.
v2: - re-add the inadvertent removal of CTX_CTRL_INHIBIT_SYN_CTX_SWITCH
- don't bother trying to document removed params on uapi header:
applications should know that from the query.
(from Chris)
v3: - disable CTX_CTRL_RS_CTX_ENABLE istead of removing it
- reword commit message after Daniele confirmed no performance
regression on his machine
- reword commit message to make clear RS is being removed due to
never been used
v4: - move I915_EXEC_RESOURCE_STREAMER to __I915_EXEC_ILLEGAL_FLAGS so
the check on ioctl() is made much earlier by
i915_gem_check_execbuffer() (suggested by Tvrtko)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180803232443.17193-1-lucas.demarchi@intel.com
On GEM side:
- GuC related fixes (Chris, Michal)
- GTT read-only pages support (Jon, Chris)
- More selftests fixes (Chris)
- More GPU reset improvements (Chris)
- Flush caches after GGTT writes (Chris)
- Handle recursive shrinker for vma->last_active allocation (Chris)
- Other execlists fixes (Chris)
On Display side:
- GLK HDMI fix (Clint)
- Rework and cleanup around HPD pin (Ville)
- Preparation work for Display Stream Compression support coming on ICL (Anusha)
- Nuke LVDS lid notification (Ville)
- Assume eDP is always connected (Ville)
- Kill intel panel detection (Ville)
Signed-off-by: Dave Airlie <airlied@redhat.com>
# gpg: Signature made Fri 20 Jul 2018 01:51:45 AM AEST
# gpg: using RSA key FA625F640EEB13CA
# gpg: Good signature from "Rodrigo Vivi <rodrigo.vivi@intel.com>"
# gpg: aka "Rodrigo Vivi <rodrigo.vivi@gmail.com>"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg: There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 6D20 7068 EEDD 6509 1C2C E2A3 FA62 5F64 0EEB 13CA
# Conflicts:
# drivers/gpu/drm/i915/intel_lrc.c
Link: https://patchwork.freedesktop.org/patch/msgid/20180719171257.GA12199@intel.com
Higlights here goes to many PSR fixes and improvements; to the Ice lake work with
power well support and begin of DSI support addition. Also there were many improvements
on execlists and interrupts for minimal latency on command submission; and many fixes
on selftests, mostly caught by our CI.
General driver:
- Clean-up on aux irq (Lucas)
- Mark expected switch fall-through for dealing with static analysis tools (Gustavo)
Gem:
- Different fixes for GuC (Chris, Anusha, Michal)
- Avoid self-relocation BIAS if no relocation (Chris)
- Improve debugging cases in on EINVAL return and vma allocation (Chris)
- Fixes and improvements on context destroying and freeing (Chris)
- Wait for engines to idle before retiring (Chris)
- Many improvements on execlists and interrupts for minimal latency on command submission (Chris)
- Many fixes in selftests, specially on cases highlighted on CI (Chris)
- Other fixes and improvements around GGTT (Chris)
- Prevent background reaping of active objects (Chris)
Display:
- Parallel modeset cleanup to fix driver reset (Chris)
- Get AUX power domain for DP main link (Imre)
- Clean-up on PSR unused func pointers (Rodrigo)
- Many PSR/PSR2 fixes and improvements (DK, Jose, Tarun)
- Add a PSR1 live status (Vathsala)
- Replace old drm_*_{un/reference} with put,get functions (Thomas)
- FBC fixes (Maarten)
- Abstract and document the usage of picking macros (Jani)
- Remove unnecessary check for unsupported modifiers for NV12. (DK)
- Interrupt fixes for display (Ville)
- Clean up on sdvo code (Ville)
- Clean up on current DSI code (Jani)
- Remove support for legacy debugfs crc interface (Maarten)
- Simplify get_encoder_power_domains (Imre)
Icelake:
- MG PLL fixes (Imre)
- Add hw workaround for alpha blending (Vandita)
- Add power well support (Imre)
- Add Interrupt Support (Anusha)
- Start to add support for DSI on Ice Lake (Madhav)
Signed-off-by: Dave Airlie <airlied@redhat.com>
# gpg: Signature made Tue 10 Jul 2018 08:41:37 AM AEST
# gpg: using RSA key FA625F640EEB13CA
# gpg: Good signature from "Rodrigo Vivi <rodrigo.vivi@intel.com>"
# gpg: aka "Rodrigo Vivi <rodrigo.vivi@gmail.com>"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg: There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 6D20 7068 EEDD 6509 1C2C E2A3 FA62 5F64 0EEB 13CA
Link: https://patchwork.freedesktop.org/patch/msgid/20180710234349.GA16562@intel.com
Across a reset, the seqno (and thus hangcheck) should restart and the
hangcheck naturally progress, for when it does not, we want to declare an
emergency. Currently, we only detect if reset and reinit fails, but we
do not detect if the call to reinit succeeds but the HW is fried - as we
are resetting hangcheck on initialisation the engine. Remove that and
rely on the natural progress to reset the hangcheck timer.
References: e21b141376 ("drm/i915: Mark the hangcheck as idle when unparking the engines")
References: 1fd00c0fae ("drm/i915: Declare the driver wedged if hangcheck makes no progress")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180709130208.11730-2-chris@chris-wilson.co.uk
Chris is doing many reworks that allow us to get full-ppgtt supported
on all platforms back to HSW. As well many other fix and improvements,
Including:
- Use GEM suspend when aborting initialization (Chris)
- Change i915_gem_fault to return vm_fault_t (Chris)
- Expand VMA to Non gem object entities (Chris)
- Improve logs for load failure, but quite logging on fault injection to avoid noise on CI (Chris)
- Other page directory handling fixes and improvements for gen6 (Chris)
- Other gtt clean-up removing redundancies and unused checks (Chris)
- Reorder aliasing ppgtt fini (Chris)
- Refactor of unsetting obg->mm.pages (Chris)
- Apply batch location restrictions before pinning (Chris)
- Ringbuffer fixes for context restore (Chris)
- Execlist fixes on freeing error pointer on allocation error (Chris)
- Make closing request flush mandatory (Chris)
- Move GEM sanitize from resume_early to resume (Chris)
- Improve debug dumps (Chris)
- Silent compiler for selftest (Chris)
- Other execlists changes to improve hangcheck and reset.
- Many gtt page directory fixes and improvements (Chris)
- Reorg context workarounds (Chris)
- Avoid ERR_PTR dereference on selftest (Chris)
Other GEM related work:
- Stop trying to reset GPU if reset failed (Mika)
- Add HW workaround for KBL to fix GPU reset (Mika)
- Fix context ban and hang accounting for client (Mika)
- Fixes on OA perf (Michel, Jani)
- Refactor on GuC log mechanisms (Piotr)
- Enable provoking vertex fix on Gen9 system (Kenneth)
More ICL patches for Display enabling:
- ICL - 10-bit support for HDMI (RK)
- ICL - Start adding TBT PLL (Paulo)
- ICL - DDI HDMK level selection (Manasi)
- ICL - GMBUS GPIO pin mapping fix (Mahesh)
- ICL - Adding DP_AUX_E support (James)
- ICL - Display interrupts handling (DK)
Other display fixes and improvements:
- Fix sprite destination color keying on SKL+ (Ville)
- Fixes and improvements on PCH detection, specially for non PCH systems (Jani)
- Document PCH_NOP (Lucas)
- Allow DBLSCAN user modes with eDP/LVDS/DSI (Ville)
- Opregion and ACPI cleanup and organization (Jani)
- Kill delays when activation psr (Rodrigo)
- ...and a consequent fix of the psr activation flow (DK)
- Fix HDMI infoframe setting (Imre)
- Fix Display interrupts and modes on old gens (Ville)
- Start switching to kernel unsigned int types (Jani)
- Introduction to Amber Lake and Whiskey Lake platforms (Jose)
- Audio clock fixes for HBR3 (RK)
- Standardize i915_reg.h definitions according to our doc and checkpatch (Paulo)
- Remove unused timespec_to_jiffies_timeout function (Arnd)
- Increase the scope of PSR wake fix for other VBTs out there (Vathsala)
- Improve debug msgs with prop name/id (Ville)
- Other clean up on unecessary cursor size defines (Ville)
- Enforce max hdisplay/hblank_start limits on HSW/BDW (Ville)
- Make ELD pointers constant (Jani)
- Fix for PSR VBT parse (Colin)
- Add warn about unsupported CDCLK rates (Imre)
Signed-off-by: Dave Airlie <airlied@redhat.com>
# gpg: Signature made Thu 21 Jun 2018 07:12:10 AM AEST
# gpg: using RSA key FA625F640EEB13CA
# gpg: Good signature from "Rodrigo Vivi <rodrigo.vivi@intel.com>"
# gpg: aka "Rodrigo Vivi <rodrigo.vivi@gmail.com>"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg: There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 6D20 7068 EEDD 6509 1C2C E2A3 FA62 5F64 0EEB 13CA
Link: https://patchwork.freedesktop.org/patch/msgid/20180625165622.GA21761@intel.com
We got a few conflicts in drm_atomic.c after merging the DRM writeback support,
now we need a backmerge to unlock develop development on drm-misc-next.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
commit b2209e62a4 ("drm/i915/execlists: Reset the CSB head tracking on
reset/sanitization") and commit 1288786b18 ("drm/i915: Move GEM sanitize
from resume_early to resume") show the conflicting requirements on the
code. We must reset the GPU before trashing live state on a fast resume
(hibernation debug, or error paths), but we must only reset our state
tracking iff the GPU is reset (or power cycled). This is tricky if we
are disabling GPU reset to simulate broken hardware; we reset our state
tracking but the GPU is left intact and recovers from its stale state.
v2: Again without the assertion for forcewake, no longer required since
commit b3ee09a4de ("drm/i915/ringbuffer: Fix context restore upon reset")
as the contexts are reset from the CS ensuring everything is powered up.
Fixes: b2209e62a4 ("drm/i915/execlists: Reset the CSB head tracking on reset/sanitization")
Fixes: 1288786b18 ("drm/i915: Move GEM sanitize from resume_early to resume")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180616202534.18767-1-chris@chris-wilson.co.uk
The discovery with trying to enable full-ppgtt was that we were
completely failing to the load both the mm and context following the
reset. Although we were performing mmio to set the PP_DIR (per-process
GTT) and CCID (context), these were taking no effect (the assumption was
that this would trigger reload of the context and restore the page
tables). It was not until we performed the LRI + MI_SET_CONTEXT in a
following context switch would anything occur.
Since we are then required to reset the context image and PP_DIR using
CS commands, we place those commands into every batch. The hardware
should recognise the no-ops and eliminate the expensive context loads,
but we still have to pay the cost of using cross-powerwell register
writes. In practice, this has no effect on actual context switch times,
and only adds a few hundred nanoseconds to no-op switches. We can improve
the latter by eliminating the w/a around known no-op switches, but there
is an ulterior motive to keeping them.
Always emitting the context switch at the beginning of the request (and
relying on HW to skip unneeded switches) does have one key advantage.
Should we implement request reordering on Haswell, we will not know in
advance what the previous executing context was on the GPU and so we
would not be able to elide the MI_SET_CONTEXT commands ourselves and
always have to emit them. Having our hand forced now actually prepares
us for later.
Now since that context and mm follow the request, we no longer (and not
for a long time since requests took over!) require a trace point to tell
when we write the switch into the ring, since it is always. (This is
even more important when you remember that simply writing into the ring
bears no relation to the current mm.)
v2: Sandybridge has to agree to use LRI as well.
Testcase: igt/drv_selftests/live_hangcheck
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180611110845.31890-1-chris@chris-wilson.co.uk
We need to move to a more flexible timeline that doesn't assume one
fence context per engine, and so allow for a single timeline to be used
across a combination of engines. This means that preallocating a fence
context per engine is now a hindrance, and so we want to introduce the
singular timeline. From the code perspective, this has the notable
advantage of clearing up a lot of mirky semantics and some clumsy
pointer chasing.
By splitting the timeline up into a single entity rather than an array
of per-engine timelines, we can realise the goal of the previous patch
of tracking the timeline alongside the ring.
v2: Tweak wait_for_idle to stop the compiling thinking that ret may be
uninitialised.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180502163839.3248-2-chris@chris-wilson.co.uk
In the future, we want to move a request between engines. To achieve
this, we first realise that we have two timelines in effect here. The
first runs through the GTT is required for ordering vma access, which is
tracked currently by engine. The second is implied by sequential
execution of commands inside the ringbuffer. This timeline is one that
maps to userspace's expectations when submitting requests (i.e. given the
same context, batch A is executed before batch B). As the rings's
timelines map to userspace and the GTT timeline an implementation
detail, move the timeline from the GTT into the ring itself (per-context
in logical-ring-contexts/execlists, or a global per-engine timeline for
the shared ringbuffers in legacy submission.
The two timelines are still assumed to be equivalent at the moment (no
migrating requests between engines yet) and so we can simply move from
one to the other without adding extra ordering.
v2: Reinforce that one isn't allowed to mix the engine execution
timeline with the client timeline from userspace (on the ring).
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180502163839.3248-1-chris@chris-wilson.co.uk
In the next patch, rings are the central timeline as requests may jump
between engines. Therefore in the future as we retire in order along the
engine timeline, we may retire out-of-order within a ring (as the ring now
occurs along multiple engines), leading to much hilarity in miscomputing
the position of ring->head.
As an added bonus, retiring along the ring reduces the penalty of having
one execlists client do cleanup for another (old legacy submission
shares a ring between all clients). The downside is that slow and
irregular (off the critical path) process of cleaning up stale requests
after userspace becomes a modicum less efficient.
In the long run, it will become apparent that the ordered
ring->request_list matches the ring->timeline, a fun challenge for the
future will be unifying the two lists to avoid duplication!
v2: We need both engine-order and ring-order processing to maintain our
knowledge of where individual rings have completed upto as well as
knowing what was last executing on any engine. And finally by decoupling
retiring the contexts on the engine and the timelines along the rings,
we do have to keep a reference to the context on each request
(previously it was guaranteed by the context being pinned).
v3: Not just a reference to the context, but we need to keep it pinned
as we manipulate the rings; i.e. we need a pin for both the manipulation
of the engine state during its retirements, and a separate pin for the
manipulation of the ring state.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180430131503.5375-3-chris@chris-wilson.co.uk
Add a selftest to ensure that we restore the whitelisted registers after
rewrite the registers everytime they might be scrubbed, e.g. module
load, reset and resume. For the other volatile workaround registers, we
export their presence via debugfs and check in igt/gem_workarounds.
However, we don't export the whitelist and rather than do so, let's test
them directly in the kernel.
The test we use is to read the registers back from the CS (this helps us
be sure that the registers will be valid for MI_LRI etc). In order to
generate the expected list, we split intel_whitelist_workarounds_emit
into two phases, the first to build the list and the second to apply.
Inside the test, we only build the list and then check that list against
the hw.
v2: Filter out pre-gen8 as they do not have RING_NONPRIV.
v3: Drop unused engine parameter, no plans to use it now or future.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Oscar Mateo <oscar.mateo@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180414122754.569-1-chris@chris-wilson.co.uk
There are different kind of workarounds (those that modify registers that
live in the context image, those that modify global registers, those that
whitelist registers, etc...) and they have different requirements in terms
of where they are applied and how. Also, by splitting them apart, it should
be easier to decide where a new workaround should go.
v2:
- Add multiple MISSING_CASE
- Rebased
v3:
- Rename mmio_workarounds to gt_workarounds (Chris, Mika)
- Create empty placeholders for BDW and CHV GT WAs
- Rebased
v4: Rebased
v5:
- Rebased
- FORCE_TO_NONPRIV register exists since BDW, so make a path
for it to achieve universality, even if empty (Chris)
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[ickle: appease checkpatch]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/1523376767-18480-2-git-send-email-oscar.mateo@intel.com
This has grown to be a sizable amount of code, so move it to
its own file before we try to refactor anything. For the moment,
we are leaving behind the WA BB code and the WAs that get applied
(incorrectly) in init_clock_gating, but we will deal with it later.
v2: Use intel_ prefix for code that deals with the hardware (Chris)
v3: Rebased
v4:
- Rebased
- New license header
v5:
- Rebased
- Added some organisational notes to the file (Chris)
v6: Include DOC section in the documentation build (Jani)
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[ickle: appease checkpatch, mostly]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/1523376767-18480-1-git-send-email-oscar.mateo@intel.com
The only usage outside the intel_lrc.c file is in the ringbuffer
init, but the irq mask calculated there is then overwritten for
all engines that have a non-zero shift, so we can drop it.
This change is not aimed at code saving but at removing from
intel_engines information that does not apply to all gens that have
the engine. When checking without the temporary WARN_ON, code size
is basically unchanged.
v2: make the irq_shifts array static const
v3: rebase, move irq_shifts array to logical_ring_default_irqs
v4: move array inside the if and use u8 for it (Chris)
Suggested-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180314182653.26981-4-daniele.ceraolospurio@intel.com
