On module load and unload, we grab the POWER_DOMAIN_INIT powerwells and
transfer them to the runtime-pm code. We can use our wakeref tracking to
verify that the wakeref is indeed passed from init to enable, and
disable to fini; and across suspend.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-17-chris@chris-wilson.co.uk

The majority of runtime-pm operations are bounded and scoped within a
function; these are easy to verify that the wakeref are handled
correctly. We can employ the compiler to help us, and reduce the number
of wakerefs tracked when debugging, by passing around cookies provided
by the various rpm_get functions to their rpm_put counterpart. This
makes the pairing explicit, and given the required wakeref cookie the
compiler can verify that we pass an initialised value to the rpm_put
(quite handy for double checking error paths).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-16-chris@chris-wilson.co.uk

Frequently, we use intel_runtime_pm_get/_put around a small block.
Formalise that usage by providing a macro to define such a block with an
automatic closure to scope the intel_runtime_pm wakeref to that block,
i.e. macro abuse smelling of python.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-15-chris@chris-wilson.co.uk

Track the temporary wakerefs used within the selftests so that leaks are
clear.

v2: Add a couple of coarse annotations for mock selftests as we now
loudly warn about the errors.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-14-chris@chris-wilson.co.uk

Keep track of the temporary rpm wakeref used for panel backlight access,
so that we can cancel it immediately upon release and so more clearly
identify leaks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-13-chris@chris-wilson.co.uk

Keep track of the temporary rpm wakeref inside hotplug detection, so
that we can cancel it immediately upon release and so clearly identify
leaks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-12-chris@chris-wilson.co.uk

Keep track of the rpm wakeref used for framebuffer access so that we can
cancel upon release and so more clearly identify leaks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-11-chris@chris-wilson.co.uk

Keep track of the temporary rpm wakerefs used for user access to the
device, so that we can cancel them upon release and clearly identify any
leaks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-10-chris@chris-wilson.co.uk

Keep track of our acquired wakeref for interacting with the guc, so that
we can cancel it upon release and so clearly identify leaks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-9-chris@chris-wilson.co.uk

Track the wakeref used for temporary access to the device, and discard
it upon release so that leaks can be identified.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-8-chris@chris-wilson.co.uk

Keep track of our wakeref used to keep the device awake so we can catch
any leak.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-7-chris@chris-wilson.co.uk

As debugfs has a simple pattern of taking a rpm wakeref around the user
access, we can track the local reference and drop it as soon as
possible.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-6-chris@chris-wilson.co.uk

As sysfs has a simple pattern of taking a rpm wakeref around the user
access, we can track the local reference and drop it as soon as
possible.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-5-chris@chris-wilson.co.uk

Keep hold of the local wakeref used in error handling, to cancel
the tracking upon release so that leaks can be identified.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-4-chris@chris-wilson.co.uk

Record the wakeref used for keeping the device awake as the GPU is
executing requests and be sure to cancel the tracking upon parking.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-3-chris@chris-wilson.co.uk

The majority of runtime-pm operations are bounded and scoped within a
function; these are easy to verify that the wakeref are handled
correctly. We can employ the compiler to help us, and reduce the number
of wakerefs tracked when debugging, by passing around cookies provided
by the various rpm_get functions to their rpm_put counterpart. This
makes the pairing explicit, and given the required wakeref cookie the
compiler can verify that we pass an initialised value to the rpm_put
(quite handy for double checking error paths).

For regular builds, the compiler should be able to eliminate the unused
local variables and the program growth should be minimal. Fwiw, it came
out as a net improvement as gcc was able to refactor rpm_get and
rpm_get_if_in_use together,

v2: Just s/rpm_put/rpm_put_unchecked/ everywhere, leaving the manual
mark up for smaller more targeted patches.
v3: Mention the cookie in Returns

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@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/20190114142129.24398-2-chris@chris-wilson.co.uk

Everytime we take a wakeref, record the stack trace of where it was
taken; clearing the set if we ever drop back to no owners. For debugging
a rpm leak, we can look at all the current wakerefs and check if they
have a matching rpm_put.

v2: Use skip=0 for unwinding the stack as it appears our noinline
function doesn't appear on the stack (nor does save_stack_trace itself!)
v3: Allow rpm->debug_count to disappear between inspections and so
avoid calling krealloc(0) as that may return a ZERO_PTR not NULL! (Mika)
v4: Show who last acquire/released the runtime pm

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Tested-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-1-chris@chris-wilson.co.uk

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

The wait-for-idle used from within the shrinker_lock_uninterruptible
depends on the struct_mutex locking state being known and declared to
i915_request_wait(). As it is conceivable that we reach the vmap
notifier from underneath struct_mutex (and so keep on relying on the
mutex_trylock_recursive), we should not blindly call i915_request_wait.

In the process we can remove the dubious polling to acquire
struct_mutex, and simply act, or not, on a successful trylock.

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/20190109164204.23935-2-chris@chris-wilson.co.uk

If the current process is being killed (it was interrupted with SIGKILL
or equivalent), it will not make any progress in page allocation and we
can abort performing the shrinking on its behalf. So we can use
mutex_lock_killable() instead (although this path should only be
reachable from kswapd currently).

Tvrtko pointed out that it should also be reachable from debugfs, which
he would prefer retain its interruptiblity. As a compromise, killable is a
step in the right direction!

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/20190109164204.23935-1-chris@chris-wilson.co.uk

If we find an incompletely setup vma inside the request/engine at the
time of a hang, it may not have vma->pages initialised, so skip
capturing the object before we iterate over NULL.

Spotted by Matthew in preparation for using unpinned vma to track engine
state.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190110111522.11023-1-chris@chris-wilson.co.uk

The only gen8+ platform that has the feature is BDW, but we don't define
the feature flag on any BDW platform and we only have partial support in
the gen8 path (irq enabling code, but no handler).
The only thing we could do in the irq handler is report the error
to userspace, but no one asked/cared about that since BDW was
released so it is relatively safe to assume that even if we added the
message no one would look at it. Just drop the dead code from the
driver instead.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
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/20190109213147.16851-1-daniele.ceraolospurio@intel.com

commit 4a15c75c ("drm/i915: Introduce per-engine workarounds")
refactored the workaround code to have functions per-engine, but didn't
call any of them from logical_xcs_ring_init. Since we do have a non-RCS
workaround for KBL (WaKBLVECSSemaphoreWaitPoll) we do need to call
intel_engine_init_workarounds for non-RCS engines.
Note that whitelist is still RCS-only.

v2: move the call to logical_ring_init (Chris)

Fixes: 4a15c75c

 ("drm/i915: Introduce per-engine workarounds")
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190110013232.8972-2-daniele.ceraolospurio@intel.com

By using the wa lists inside the live driver structures, we won't
catch issues where those are incorrectly setup or corrupted.
To cover this gap, update the workaround framework to allow saving the
wa lists to independent structures and use them in the selftests.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190110013232.8972-1-daniele.ceraolospurio@intel.com
[tursulin: Fixup checkpatch whitespace complaint in memset.]

In the continual quest to reduce the amount of global work required when
submitting requests, replace i915_retire_requests() after allocation
failure to retiring just our ring.

v2: Don't forget the list iteration included an early break, so we would
never throttle on the last request in the ring/timeline.
v3: Use the common ring_retire_requests()

References: 11abf0c5

 ("drm/i915: Limit the backpressure for i915_request allocation")
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/20190109215932.26454-1-chris@chris-wilson.co.uk

Add support for PMIC MIPI sequences using the new
intel_soc_pmic_exec_mipi_pmic_seq_element function.

This fixes the DSI LCD panel not lighting up when not initialized by the
GOP (because an external monitor was connected) on GPD win and GPD pocket
devices.

Specifically the LCD panel seems to need GPIO pin 9 on the PMIC to be
driven high, which is done through a PMIC MIPI sequence. Before this commit
if the sequence was not executed by the GOP the pin would stay low causing
the LCD panel to not work. Having the MIPI sequences properly control this
GPIO should also help save some power when the panel is off.

Changes in v2, v3:
-Only changes to other patches in this patch-set

Changes in v4:
-Move decoding of the raw 15 bytes PMIC MIPI sequence element into
 i2c-address, register-address, value and mask into the mipi_exec_pmic()
 function instead of passing the raw data to
 intel_soc_pmic_exec_mipi_pmic_seq_element()

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190107111556.4510-5-hdegoede@redhat.com

Most PMIC-s use only a single i2c-address, so after verifying the
i2c-address matches, we can simply pass the call to regmap_update_bits.

This commit adds support for this and hooks this up for the xpower AXP288
PMIC by setting the new pmic_i2c_address field.

This fixes the following errors on display on / off on a Jumper Ezpad
mini 3 and an Onda V80 plus tablet, both of which use the AXP288:

intel_soc_pmic_exec_mipi_pmic_seq_element: Not implemented
intel_soc_pmic_exec_mipi_pmic_seq_element: i2c-addr: 0x34 reg-addr ...
[drm:mipi_exec_pmic [i915]] *ERROR* mipi_exec_pmic failed, error: -95

Instead of these errors on both devices we now correctly turn on / off
DLDO3 (through direct register manipulation). On the Onda V80 plus this
fixes an issue with the backlight being brighter around the borders after
an off / on cycle. This should also help to save some power when the
display is off.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190107111556.4510-4-hdegoede@redhat.com

Implement the exec_mipi_pmic_seq_element callback for the CHT Whiskey Cove
PMIC.

On some CHT devices this fixes the LCD panel not lighting up when it was
not initialized by the GOP, because an external monitor was plugged in and
the GOP initialized only the external monitor.

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190107111556.4510-3-hdegoede@redhat.com

DSI LCD panels describe an initialization sequence in the Video BIOS
Tables using so called MIPI sequences. One possible element in these
sequences is a PMIC specific element of 15 bytes.

Although this is not really an ACPI opregion, the ACPI opregion code is the
closest thing we have. We need to have support for these PMIC specific MIPI
sequence elements somwhere. Since we already instantiate a special platform
device for Intel PMICs for the ACPI PMIC OpRegion handler to bind to,
with PMIC specific implementations of the OpRegion, the handling of MIPI
sequence PMIC elements fits very well in the ACPI PMIC OpRegion code.

This commit adds a new intel_soc_pmic_exec_mipi_pmic_seq_element()
function, which is to be backed by a PMIC specific
exec_mipi_pmic_seq_element callback. This function will be called by the
i915 code to execture MIPI sequence PMIC elements.

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190107111556.4510-2-hdegoede@redhat.com

Needs just a few additional includes here and there.

Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190108082709.3748-1-jani.nikula@intel.com

If we haven't shipped and enabled firmware for a particular platform,
there is nothing the user can do about it. Don't scare the user with an
unactionable, unidentifiable warning!

<6> [310.769452] i915 0000:00:02.0: GuC: No firmware known for this platform!
<4> [310.769458] [drm] HuC: No firmware known for this platform!

Unify both GuC/HuC messages to include the device for which we lack the
firmware, and provide the platform name as an aide-memoire.

v2: Move and refine the message to common site of intel_uc_fw_fetch.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190108150246.1471-1-chris@chris-wilson.co.uk

Minimal change to nuke the static buf.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190107145149.10069-1-jani.nikula@intel.com

Ignore trying to shrink from i915 if we fail to acquire the struct_mutex
in the shrinker while performing direct-reclaim. The trade-off being
(much) lower latency for non-i915 clients at an increased risk of being
unable to obtain a page from direct-reclaim without hitting the
oom-notifier. The proviso being that we still keep trying to hard
obtain the lock for kswapd so that we can reap under heavy memory
pressure.

v2: Taint all mutexes taken within the shrinker with the struct_mutex
subclass as an early warning system, and drop I915_SHRINK_ACTIVE from
vmap to reduce the number of dangerous paths. We also have to drop
I915_SHRINK_ACTIVE from oom-notifier to be able to make the same claim
that ACTIVE is only used from outside context, which fits in with a
longer strategy of avoiding stalls due to scanning active during
shrinking.

The danger in using the subclass struct_mutex is that we declare
ourselves more knowledgable than lockdep and deprive ourselves of
automatic coverage. Instead, we require ourselves to mark up any mutex
taken inside the shrinker in order to detect lock-inversion, and if we
miss any we are doomed to a deadlock at the worst possible moment.

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/20190107115509.12523-1-chris@chris-wilson.co.uk

Generally catch up with 5.0-rc1, and specifically get the changes:

96d4f267 ("Remove 'type' argument from access_ok() function")
0b2c8f8b ("i915: fix missing user_access_end() in page fault exception case")
594cc251

 ("make 'user_access_begin()' do 'access_ok()'")

Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Merge tag 'topic/drmp-cleanup-2019-01-02' of git://anongit.freedesktop.org/drm/drm-intel into drm-intel-next-queued

Make some drm headers self-contained with includes and forward
declarations.

This topic branch has already been merged to drm-misc-next as commit
1c95f662

 ("Merge tag 'topic/drmp-cleanup-2019-01-02' of
git://anongit.freedesktop.org/drm/drm-intel into drm-misc-next"). Now
merge it to drm-intel-next-queued to unblock some further drmP.h cleanup
without having to wait for a backmerge.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
From: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/87pntfl6pa.fsf@intel.com

Being a mock device, we suffer no DMA restrictions, so set the coherent
mask to 64b.

v2: Fix up mock_huge_selftests

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109243
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190107181856.23789-1-chris@chris-wilson.co.uk

Include the total size of closed vma when reporting the per_ctx_stats of
debugfs/i915_gem_objects.

Whilst adjusting the context tracking, note that we can simply use our
list of contexts in i915->contexts rather than circumlocute via
dev->filelist and the per-file context idr, with the result that we can
show objects allocated to different vm (i.e. contexts within a file).

We change the output to show every context of each client, with its own
unique set of objects (for full-ppgtt machines, i.e. gen7+, for older
hardware all objects are in the global gtt and so can not be associated
with a single context). That should result in no loss of information,
and for gen7+, no duplication of active objects.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190107115509.12523-2-chris@chris-wilson.co.uk

Haswell also requires the RING_IMR flush for its unique vebox setup to
avoid losing interrupts, as per 476af9c2 ("drm/i915/gen6: Flush
RING_IMR changes before changing the global GT IMR"):

On Baytail, notably, we can still detect missed interrupt syndrome
(where we never spot a completed request). In this case, it can be
alleviated by always keeping the interrupt unmasked, implying that the
interrupt is being lost in the window after modifying the IMR. (This is
the reason we still have the posting reads on enable_irq, if we remove
them we miss interrupts!) Having narrowed the issue down to the IMR,
rather than keeping it always enabled, applying the usual posting
read/flush of the RING_IMR before unmasking the GT IMR also seems to
prevent the missed interrupt. So be it.

References: 476af9c2

 ("drm/i915/gen6: Flush RING_IMR changes before changing the global GT IMR")
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/20190105115647.4970-1-chris@chris-wilson.co.uk

CC [M]  drivers/gpu/drm/i915/intel_device_info.o
drivers/gpu/drm/i915/intel_device_info.c:727: warning: Function parameter or member 'dev_priv' not described in 'intel_device_info_runtime_init'
drivers/gpu/drm/i915/intel_device_info.c:727: warning: Excess function parameter 'info' description in 'intel_device_info_runtime_init'

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190105014652.3472-1-chris@chris-wilson.co.uk