This is a complicated one. Essentially, there's currently a problem in the MST
core that hasn't really caused any issues that we're aware of (emphasis on "that
we're aware of"): locking.
When we go through and probe the link addresses and path resources in a
topology, we hold no locks when updating ports with said information. The
members I'm referring to in particular are:
- ldps
- ddps
- mcs
- pdt
- dpcd_rev
- num_sdp_streams
- num_sdp_stream_sinks
- available_pbn
- input
- connector
Now that we're handling UP requests asynchronously and will be using some of
the struct members mentioned above in atomic modesetting in the future for
features such as PBN validation, this is going to become a lot more important.
As well, the next few commits that prepare us for and introduce suspend/resume
reprobing will also need clear locking in order to prevent from additional
racing hilarities that we never could have hit in the past.
So, let's solve this issue by using &mgr->base.lock, the modesetting
lock which currently only protects &mgr->base.state. This works
perfectly because it allows us to avoid blocking connection_mutex
unnecessarily, and we can grab this in connector detection paths since
it's a ww mutex. We start by having drm_dp_mst_handle_up_req() hold this
when updating ports. For drm_dp_mst_handle_link_address_port() things
are a bit more complicated. As I've learned the hard way, we can grab
&mgr->lock.base for everything except for port->connector. See, our
normal driver probing paths end up generating this rather obvious
lockdep chain:
&drm->mode_config.mutex
-> crtc_ww_class_mutex/crtc_ww_class_acquire
-> &connector->mutex
However, sysfs grabs &drm->mode_config.mutex in order to protect itself
from connector state changing under it. Because this entails grabbing
kn->count, e.g. the lock that the kernel provides for protecting sysfs
contexts, we end up grabbing kn->count followed by
&drm->mode_config.mutex. This ends up creating an extremely rude chain:
&kn->count
-> &drm->mode_config.mutex
-> crtc_ww_class_mutex/crtc_ww_class_acquire
-> &connector->mutex
I mean, look at that thing! It's just evil!!! This gross thing ends up
making any calls to drm_connector_register()/drm_connector_unregister()
impossible when holding any kind of modesetting lock. This is annoying
because ideally, we always want to ensure that
drm_dp_mst_port->connector never changes when doing an atomic commit or
check that would affect the atomic topology state so that it can
reliably and easily be used from future DRM DP MST helpers to assist
with tasks such as scanning through the current VCPI allocations and
adding connectors which need to have their allocations updated in
response to a bandwidth change or the like.
Being able to hold &mgr->base.lock throughout the entire link probe
process would have been _great_, since we could prevent userspace from
ever seeing any states in-between individual port changes and as a
result likely end up with a much faster probe and more consistent
results from said probes. But without some rework of how we handle
connector probing in sysfs it's not at all currently possible. In the
future, maybe we can try using the sysfs locks to protect updates to
connector probing state and fix this mess.
So for now, to protect everything other than port->connector under
&mgr->base.lock and ensure that we still have the guarantee that atomic
check/commit contexts will never see port->connector change we use a
silly trick. See: port->connector only needs to change in order to
ensure that input ports (see the MST spec) never have a ghost connector
associated with them. But, there's nothing stopping us from simply
throwing the entire port out and creating a new one in order to maintain
that requirement while still keeping port->connector consistent across
the lifetime of the port in atomic check/commit contexts. For all
intended purposes this works fine, as we validate ports in any contexts
we care about before using them and as such will end up reporting the
connector as disconnected until it's port's destruction finalizes. So,
we just do that in cases where we detect port->input has transitioned
from true->false. We don't need to worry about the other direction,
since a port without a connector isn't visible to userspace and as such
doesn't need to be protected by &mgr->base.lock until we finish
registering a connector for it.
For updating members of drm_dp_mst_port other than port->connector, we
simply grab &mgr->base.lock in drm_dp_mst_link_probe_work() for already
registered ports, update said members and drop the lock before
potentially registering a connector and probing the link address of it's
children.
Finally, we modify drm_dp_mst_detect_port() to take a modesetting lock
acquisition context in order to acquire &mgr->base.lock under
&connection_mutex and convert all it's users over to using the
.detect_ctx probe hooks.
With that, we finally have well defined locking.
Changes since v4:
* Get rid of port->mutex, stop using connection_mutex and just use our own
modesetting lock - mgr->base.lock. Also, add a probe_lock that comes
before this patch.
* Just throw out ports that get changed from an output to an input, and
replace them with new ports. This lets us ensure that modesetting
contexts never see port->connector go from having a connector to being
NULL.
* Write an extremely detailed explanation of what problems this is
trying to fix, since there's a _lot_ of context here and I honestly
forgot some of it myself a couple times.
* Don't grab mgr->lock when reading port->mstb in
drm_dp_mst_handle_link_address_port(). It's not needed.
Cc: Juston Li <juston.li@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022023641.8026-7-lyude@redhat.com
Currently, MST lacks locking in a lot of places that really should have
some sort of locking. Hotplugging and link address code paths are some
of the offenders here, as there is actually nothing preventing us from
running a link address probe while at the same time handling a
connection status update request - something that's likely always been
possible but never seen in the wild because hotplugging has been broken
for ages now (with the exception of amdgpu, for reasons I don't think
are worth digging into very far).
Note: I'm going to start using the term "in-memory topology layout" here
to refer to drm_dp_mst_port->mstb and drm_dp_mst_branch->ports.
Locking in these places is a little tougher then it looks though.
Generally we protect anything having to do with the in-memory topology
layout under &mgr->lock. But this becomes nearly impossible to do from
the context of link address probes due to the fact that &mgr->lock is
usually grabbed under random various modesetting locks, meaning that
there's no way we can just invert the &mgr->lock order and keep it
locked throughout the whole process of updating the topology.
Luckily there are only two workers which can modify the in-memory
topology layout: drm_dp_mst_up_req_work() and
drm_dp_mst_link_probe_work(), meaning as long as we prevent these two
workers from traveling the topology layout in parallel with the intent
of updating it we don't need to worry about grabbing &mgr->lock in these
workers for reads. We only need to grab &mgr->lock in these workers for
writes, so that readers outside these two workers are still protected
from the topology layout changing beneath them.
So, add the new &mgr->probe_lock and use it in both
drm_dp_mst_link_probe_work() and drm_dp_mst_up_req_work(). Additionally,
add some more detailed explanations for how this locking is intended to
work to drm_dp_mst_port->mstb and drm_dp_mst_branch->ports.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Sean Paul <sean@poorly.run>
Cc: Juston Li <juston.li@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022023641.8026-6-lyude@redhat.com
Once upon a time, hotplugging devices on MST branches actually worked in
DRM. Now, it only works in amdgpu (likely because of how it's hotplug
handlers are implemented). On both i915 and nouveau, hotplug
notifications from MST branches are noticed - but trying to respond to
them causes messaging timeouts and causes the whole topology state to go
out of sync with reality, usually resulting in the user needing to
replug the entire topology in hopes that it actually fixes things.
The reason for this is because the way we currently handle UP requests
in MST is completely bogus. drm_dp_mst_handle_up_req() is called from
drm_dp_mst_hpd_irq(), which is usually called from the driver's hotplug
handler. Because we handle sending the hotplug event from this function,
we actually cause the driver's hotplug handler (and in turn, all
sideband transactions) to block on
drm_device->mode_config.connection_mutex. This makes it impossible to
send any sideband messages from the driver's connector probing
functions, resulting in the aforementioned sideband message timeout.
There's even more problems with this beyond breaking hotplugging on MST
branch devices. It also makes it almost impossible to protect
drm_dp_mst_port struct members under a lock because we then have to
worry about dealing with all of the lock dependency issues that ensue.
So, let's finally actually fix this issue by handling the processing of
up requests asyncronously. This way we can send sideband messages from
most contexts without having to deal with getting blocked if we hold
connection_mutex. This also fixes MST branch device hotplugging on i915,
finally!
Cc: Juston Li <juston.li@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022023641.8026-5-lyude@redhat.com
Since we're going to be implementing suspend/resume reprobing very soon,
we need to make sure we are extra careful to ensure that our locking
actually protects the topology state where we expect it to. Turns out
this isn't the case with drm_dp_port_setup_pdt() and
drm_dp_port_teardown_pdt(), both of which change port->mstb without
grabbing &mgr->lock.
Additionally, since most callers of these functions are just using it to
teardown the port's previous PDT and setup a new one we can simplify
things a bit and combine drm_dp_port_setup_pdt() and
drm_dp_port_teardown_pdt() into a single function:
drm_dp_port_set_pdt(). This function also handles actually ensuring that
we grab the correct locks when we need to modify port->mstb.
Cc: Juston Li <juston.li@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022023641.8026-4-lyude@redhat.com
When reprobing an MST topology during resume, we have to account for the
fact that while we were suspended it's possible that mstbs may have been
removed from any ports in the topology. Since iterating downwards in the
topology requires that we hold &mgr->lock, destroying MSTBs from this
context would result in attempting to lock &mgr->lock a second time and
deadlocking.
So, fix this by first moving destruction of MSTBs into
destroy_connector_work, then rename destroy_connector_work and friends
to reflect that they now destroy both ports and mstbs.
Note that even though this means that MSTBs will still be accessible for
a short period of time between their removal from the topology and
delayed destruction, we are still protected against referencing a MSTB
with a refcount of 0 since we use kref_get_unless_zero() in most places.
Changes since v1:
* s/destroy_connector_list/destroy_port_list/
s/connector_destroy_lock/delayed_destroy_lock/
s/connector_destroy_work/delayed_destroy_work/
s/drm_dp_finish_destroy_branch_device/drm_dp_delayed_destroy_mstb/
s/drm_dp_finish_destroy_port/drm_dp_delayed_destroy_port/
- danvet
* Use two loops in drm_dp_delayed_destroy_work() - danvet
* Better explain why we need to do this - danvet
* Use cancel_work_sync() instead of flush_work() - flush_work() doesn't
account for work requeing
Cc: Juston Li <juston.li@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022023641.8026-2-lyude@redhat.com
Thierry needs fd70c7755b ("drm/bridge: tc358767: fix max_tu_symbol
value") to be able to merge his dp_link patch series.
Some adjacent changes conflicts, plus some clashes in i915 due to
cherry-picking and git trying to be helpful and leaving both versions
in.
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
As per the display enable sequence, we need to follow the enable sequence
for slaves first with DP_TP_CTL set to Idle and configure the transcoder
port sync register to select the corersponding master, then follow the
enable sequence for master leaving DP_TP_CTL to idle.
At this point the transcoder port sync mode is configured and enabled
and the Vblanks of both ports are synchronized so then set DP_TP_CTL
for the slave and master to Normal and do post crtc enable updates.
v11:
* Rebase (Manasi)
v10:
* in trans sync mode, dont stop link train for tgl (Manasi)
v9:
Remove update_scanline_offset to rebase on Maarten's patch (Manasi)
v8:
* Rebase on Maarten's patches (Manasi)
v7:
* Use ffs(slaves) to get slave crtc (Ville)
v6:
* Modeset implies active_changed, remove one condition (Maarten)
v5:
* Fix checkpatch warning (Manasi)
v4:
* Reuse skl_commit_modeset_enables() hook (Maarten)
* Obtain slave crtc and states from master (Maarten)
v3:
* Rebase on drm-tip (Manasi)
v2:
* Create a icl_update_crtcs hook (Maarten, Danvet)
* This sequence only for CRTCs in trans port sync mode (Maarten)
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191018172725.1338-4-manasi.d.navare@intel.com
After the state is committed, we readout the HW registers and compare
the HW state with the SW state that we just committed.
For Transcdoer port sync, we add master_transcoder and the
salves bitmask to the crtc_state, hence we need to read those during
the HW state readout to avoid pipe state mismatch.
v11:
* Move master trans init to get pipe_Config hooks (Ville)
v10:
* Initialize master_tarnscoder readout for all platforms (Ville)
v9:
* Initialize master_transcoder = INVALID at get config (Ville)
v8:
* Use master_select -1, address TRANS_EDP case (Ville)
* Rename master_transcoder to _readout (Lucas)
v7:
* NDont read HW state for DSI
v6:
* Go through both parts of HW readout (Maarten)
* Add a WARN if the same trans configured as
master and slave (Ville, Maarten)
v5:
* Add return INVALID in defaut case (Maarten)
v4:
* Get power domains in master loop for get_config (Ville)
v3:
* Add TRANSCODER_D (Maarten)
* v3 Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
v2:
* Add Transcoder_D and MISSING_CASE (Maarten)
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191018172725.1338-3-manasi.d.navare@intel.com
In case of tiled displays where different tiles are displayed across
different ports, we need to synchronize the transcoders involved.
This patch implements the transcoder port sync feature for
synchronizing one master transcoder with one or more slave
transcoders. This is only enbaled in slave transcoder
and the master transcoder is unaware that it is operating
in this mode.
This has been tested with tiled display connected to ICL.
v7:
* Rebase on Maarten's patches
v6:
* Use master_trans +1 and address missing trans_edp case (Ville)
v5:
* Add TRANSCODER_D case and MISSING_CASE (Maarten)
v4:
Rebase
v3:
* Check of DP_MST moved to atomic_check (Maarten)
v2:
* Do not use RMW, just write to the register in commit (Jani N)
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191018172725.1338-2-manasi.d.navare@intel.com
In case of tiled displays when the two tiles are sent across two CRTCs
over two separate DP SST connectors, we need a mechanism to synchronize
the two CRTCs and their corresponding transcoders.
So use the master-slave mode where there is one master corresponding
to last horizontal and vertical tile that needs to be genlocked with
all other slave tiles.
This patch identifies saves the master transcoder in all the slave
CRTC states. This is needed to select the master CRTC/transcoder
while configuring transcoder port sync for the corresponding slaves.
v6:
Rebase (manasi)
v5:
* Address Ville's comments
* Just pass crtc_state, no need to check GEN (Ville)
v4:
* Rebase
v3:
* Use master_tramscoder instead of master_crtc for valid
HW state readouts (Ville)
v2:
* Move this to intel_mode_set_pipe_config(Jani N, Ville)
* Use slave_bitmask to save associated slaves in master crtc state (Ville)
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191018172725.1338-1-manasi.d.navare@intel.com
Commit 2d6f6f359f ("drm/i915: add i915_driver_modeset_remove()")
claimed removal of asymmetry in probe() and remove() calls, however, it
didn't take care of calling intel_irq_uninstall() on driver remove.
That doesn't hurt as long as we still call it from
intel_modeset_driver_remove() but in order to have full symmetry we
should call it again from i915_driver_modeset_remove().
Note that it's safe to call intel_irq_uninstall() twice thanks to
commit b318b82455 ("drm/i915: Nuke drm_driver irq vfuncs"). We may
only want to mention the case we are adding in a related FIXME comment
provided by that commit. While being at it, update the name of
function mentioned as calling it out of sequence as that name has been
changed meanwhile by commit 78dae1ac35 ("drm/i915: Propagate
"_remove" function name suffix down").
Suggested-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/6250061.7lZMOAyebC@jkrzyszt-desk.ger.corp.intel.com
All the timeout values fit in u16, so let's shrink the structure
a bit.
This ends up actually increasing the .text size a bit due to
some changes in instructions (constant imul+small jmps replaced
with mov+bigger jmpqs). Seems pretty arbitrary to me so I'll
just pretend I didn't see it.
text data bss dec hex filename
- 34521 360 0 34881 8841 intel_hdmi.o
+ 34537 360 0 34897 8851 intel_hdmi.o
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191010145127.7487-5-ville.syrjala@linux.intel.com
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
The only reason for the timeout2 value in the array is the
HDCP_2_2_AKE_SEND_HPRIME message. But that one still needs
special casing inside the loop, and so just ends up making
the code harder to read. Let's just remove this leaky
timeout2 abstraction and special case that one command
in a way that is easy to understand. We can then remove the
timeout2 member from struct entirely.
text data bss dec hex filename
- 34633 360 0 34993 88b1 intel_hdmi.o
+ 34521 360 0 34881 8841 intel_hdmi.o
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191010145127.7487-4-ville.syrjala@linux.intel.com
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Unlike other planes the cursor currently handles 180 degree rotation
adjustment during the hardware programming phase. Let's move that
stuff into intel_cursor_check_surface() to match how we do things
with other plane types.
And while at we'll plop in the final src x/y coordinates (which will
actually always be zero) into the src rect and color_plane[0].x/y,
just for some extra consistency.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191015152757.12231-1-ville.syrjala@linux.intel.com
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Normally, we try and skip submission if ELSP[1] is filled. However, we
may desire to enable timeslicing due to the queue priority, even if
ELSP[1] itself does not require timeslicing. That is the queue is equal
priority to ELSP[0] and higher priority then ELSP[1]. Previously, we
would wait until the context switch to preempt the current ELSP[1], but
with timeslicing, we want to preempt ELSP[0] and replace it with the
queue.
In writing the test case, it become quickly apparent that we were also
suppressing the tasklet during promotion and so failing to notice when
the queue started requiring timeslicing.
Fixes: 2229adc813 ("drm/i915/execlist: Trim immediate timeslice expiry")
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/20191018072027.31948-1-chris@chris-wilson.co.uk
Medium term goal is to eliminate the i915->engine[] array and to get there
we have recently introduced equivalent array in intel_gt. Now we need to
migrate the code further towards this state.
This next step is to eliminate usage of i915->engines[] from the
for_each_engine_masked iterator.
For this to work we also need to use engine->id as index when populating
the gt->engine[] array and adjust the default engine set indexing to use
engine->legacy_idx instead of assuming gt->engines[] indexing.
v2:
* Populate gt->engine[] earlier.
* Check that we don't duplicate engine->legacy_idx
v3:
* Work around the initialization order issue between default_engines()
and intel_engines_driver_register() which sets engine->legacy_idx for
now. It will be fixed properly later.
v4:
* Merge with forgotten v2.5.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@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/20191017161852.8836-1-tvrtko.ursulin@linux.intel.com
The locks (active.lock and rq->lock) need to be taken with disabled
interrupts. This is done in i915_request_retire() by disabling the
interrupts independently of the locks itself.
While local_irq_disable()+spin_lock() equals spin_lock_irq() on vanilla
it does not on PREEMPT_RT.
Chris Wilson confirmed that local_irq_disable() was just introduced as
an optimisation to avoid enabling/disabling interrupts during
lock/unlock combo.
Enable/disable interrupts as part of the locking instruction.
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191017161352.e5z3ugse7gxl5ari@linutronix.de
