Continue abstracting hotplug storm related functions to clarify the
code. This time, abstract hotplug irq storm related hotplug
disabling. While at it, clean up the loop iterating over connectors for
readability.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The hotplug work function has two loops iterating over connectors, the
first for handling hotplug disabling due to irq storms and the second
for actually handling the hotplug events. Move the debug printing into
the second one, so we can abstract the storm handling better. This may
change the output ordering slightly when there are multiple simultaneous
hotplug events.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

intel_crtc->config will be removed eventually, so use crtc->hwmode.
drm_atomic_helper_update_legacy_modeset_state updates hwmode,
but crtc->active will eventually be gone too. Set dotclock to zero
to indicate the crtc is inactive.

Changes since v1:
- With the hwmode update in drm*update_legacy_modeset_state removed,
  intel_modeset_update_state has to assign it instead.
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

crtc_state->enable means a crtc is configured, but it may be turned
off for dpms. Until the commit "use intel_crtc_control everywhere"
crtc_state->active was not updated on crtc off, but now
crtc_state->active should be used for tracking whether a crtc is
scanning out or not.

A few commits from now dpms will be handled by calling
intel_set_mode with a different value for crtc_state->active,
which causes a crtc to turn on or off.

At this point crtc->active should mirror crtc_state->active,
so some paranoia from the crtc_disable functions can be removed.

intel_set_mode_setup_plls still checks for ->enable, because all
resources that are needed have to be calculated, else
dpms changes may not succeed.
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

Simplify intel_hpd_irq_handler() by extracting HPD irq storm detection
to a separate function.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The hotplug status is cached in hp_control, and will be passed on to
bottom halves through intel_hpd_irq_handler(), so we can clear the
sticky bits earlier.

While at it, drop the redundant logging of the hotplug status, which
will also be logged by pch_get_hpd_pins().
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Split intel_hpd_irq_handler into platforms specific and platform
agnostic parts. The platform specific parts decode the registers into
information about which hpd pins triggered, and if they were long
pulses. The platform agnostic parts do further processing, such as
interrupt storm mitigation and scheduling bottom halves.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

As the hpd loops have been merged together, we don't have to maintain
state for all hpd triggers.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Nothing in the two consecutive loops over hpd pins depends on state in a
larger context than the single hpd pin. If we skip the rest of the loop
on short hpd pulses, we can merge the two loops into one.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

In an unfortunate back and forth stepping, retract the earlier change to
reduce indent. This is to make merging the two loops easier. No
functional changes.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Multiple positive and negative checks for hpd[i] & hotplug_trigger gets
hard to read. Simplify. This should make follow-up patches merging the
two loops easier. No functional changes.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

No functional changes.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

There are plenty of hotplug related fields in struct drm_i915_private
scattered all around. Group them under one hotplug struct. Clean up
naming while at it. No functional changes.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Continue to loop early if there's nothing to do. No functional changes.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Move dp aux irq handling within the same branch instead of duplicating
the conditions. No functional changes.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Bail out early if nothing to do. No functional changes.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

In commit 1854d5ca
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Apr 7 16:20:32 2015 +0100

    drm/i915: Deminish contribution of wait-boosting from clients

we removed an atomic timer based check for allowing waitboosting and
moved it below the mutex taken during RPS. However, that mutex can be
held for long periods of time on Vallyview/Cherryview as communication
with the PCU is slow. As clients may frequently wait for results (e.g.
such as tranform feedback) we introduced contention between the client
and the RPS worker. We can take advantage of the RPS worker, by
switching the wait boost decision to use spin locks and defer the
actual reclocking to the worker.

Fixes a regression of up to 45% on Baytrail and Baswell!

v2 (Daniel):
- Use max_freq_softlimit instead of the not-yet-merged boost
  frequency.
- Don't inject a fake irq into the boost work, instead treat
  client_boost as just another legit waker.

v3: Drop the now unused mask (Chris).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90112
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> (v1)
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

If we have clients stalled waiting for requests, ignore the GPU if it
signals that it should downclock due to low load. This helps prevent
the automatic timeout from causing extremely long running batches from
taking even longer.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Use HOTPLUG_INT_STATUS_G4X instead of HOTPLUG_INT_STATUS_I915 on VLV/CHV
so that we don't confuse the AUX status bits with SDVO status bits.

Avoid pointless log spam as below while handling AUX interrupts:
[drm:intel_hpd_irq_handler] hotplug event received, stat 0x00000040, dig 0x00000000
[drm:intel_hpd_irq_handler] hotplug event received, stat 0x00000040, dig 0x00000000
[drm:intel_hpd_irq_handler] hotplug event received, stat 0x00000040, dig 0x00000000
[drm:intel_hpd_irq_handler] hotplug event received, stat 0x00000040, dig 0x00000000
[drm:intel_hpd_irq_handler] hotplug event received, stat 0x00000040, dig 0x00000000
[drm:intel_dp_aux_ch] dp_aux_ch timeout status 0x71450064

Note that there's no functional issue, it's just that the sdvo bits
overlap with the dp aux bits. Hence every time we receive an aux
interrupt we also think there's an sdvo hpd interrupt, but due to lack
of any sdvo encoders nothing ever happens because of that.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
[danvet: Add Ville's explanation why nothing functional really
changes.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Remove some inline keywords. One of the functions has clearly outgrown
it anyway, so let's just leave it to the compiler.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

We stopped handling them in

commit aaecdf61
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Tue Nov 4 15:52:22 2014 +0100

    drm/i915: Stop gathering error states for CS error interrupts

but just clearing is apparently not enough: A sufficiently dead gpu
left behind by firmware (*cough* coreboot *cough*) can keep the gpu in
an endless loop of such interrupts, eventually leading to the nmi
firing. And definitely to what looks like a machine hang.

Since we don't even enable these interrupts on gen5+ let's do the same
on earlier platforms.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=93171Tested-by: NMono <mono-for-kernel-org@donderklumpen.de>
Tested-by: info@gluglug.org.uk
Cc: stable@vger.kernel.org
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

GMBUS interrupt has been moved to CPU side in BXT.
What this patch does is:
1. Enable GMBUS IRQ in de_post_install function
2. Handle this interrupt as a port interrupt in display irq
   handler

v2: Rebase on top of the for_each_pipe() change adding dev_priv as
    first argument (Damien).
v3: read BXT_DE_PORT_GMBUS IIR flag only on BXT on other platforms
    it's reserved (imre)
v4: (jani)
- remove redundant 'BXT GMBUS' comment
- fix formatting of BXT_DE_PORT_GMBUS definition
Reviewed-by: NSatheeshakrishna M <satheeshakrishna.m@intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com> (v1)
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

This patch adds conditional checks in gen8_irq functions
to support BXT. Most of the checks just look for PCH split
availability, and block the call to PCH interrupt functions if
not available.

v2: (jani)
- drop redundant TODO comment about PCH IRQ flags on BXT
- check HAS_PCH_SPLIT instead of IS_BROXTON when handling PCH specific
  IRQ events in gen8_irq_handler()
- check HAS_PCH_SPLIT before calling the function instead of a
  corresponding early return within the called function for
  ibx_irq_reset(), ibx_irq_pre_postinstall(), ibx_irq_postinstall()
v3: (jani)
- in ironlake_irq_postinstall() and ironlake_irq_reset() HAS_PCH_SPLIT
  is always true, so drop the check for it
Reviewed-by: NSatheeshakrishna M <satheeshakrishna.m@intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Shashank Sharma <ppashank.sharma@intel.com> (v1)
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

This patch adds a hot plug interrupt handler function for BXT.
What this function typically does is:
1. Check if hot plug is enabled from hot plug control register.
2. Call hpd_irq_handler with appropriate trigger to detect a
   plug storm and schedule a bottom half.
3. Clear sticky status bits in hot plug control register..

v2: (jani)
- drop redundant unlikely()
- s/Todo/FIXME:/ in code comment
- declare 'found' var in the scope where it's used
- check for IS_BROXTON before handling BXT_DE_PORT_HOTPLUG_MASK
Reviewed-by: NSatheeshakrishna M <satheeshakrishna.m@intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com> (v1)
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

All non-GMCH platforms have the same register layout for HPD long/short
status, so let's use this condition instead of HAS_PCH_SPLIT, as the
latter doesn't apply for BXT.

Noticed by Daniel.
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

In BXT, DDI hotplug control has been moved to CPU from PCH.
This patch adds a new IRQ setup function for BXT which:
1. Checks which HPD ports are requested to be enabled by encoders.
2. Enables those ports in the hot plug control register.
3. Un-masks these port interrupts in the IMR register.
4. Enables these port interrupts in the IER register.

V3: Kept the default HPD filter count to default (500 us) as per
    satheesh's comment
v4: Remove unused HPD filter defines (Damien)
v5: warn if trying to setup HPD on port A (imre)
v6: fix order of definitions for register bitfields (Daniel)
v7: (jani)
- define the size of the hpd_bxt array explicitly for bound checking
- use for_each_intel_encoder instead of open coding it
- fix format/order of definitions for BXT_HOTPLUG_CTL reg bitfields
Reviewed-by: NSatheeshakrishna M <satheeshakrishna.m@intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com> (v4)
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Remove some needless variables and parameter passing.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Similar in vain in reducing the number of unrequired spinlocks used for
execlist command submission (where the forcewake is required but
manually controlled), we know that the IRQ registers are outside of the
powerwell and so we can access them directly. Since we now have direct
access exported via I915_READ_FW/I915_WRITE_FW, lets put those to use in
the irq handlers as well.

In the process, reorder the execlist submission to happen as early as
possible.

v2: Restrict the untraced register mmio to just the GT path (i.e. the
hotpath for execlists)
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The issue is that by computing the last_adj value after applying the
clamping, we can end up with a bogus value for feeding into the next RPS
autotuning step.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: NDeepak S <deepak.s@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Reuse the same reclocking strategy for Baytail as on its bigger brethren,
Sandybridge and Ivybridge. In particular, this makes the device quicker
to reclock (both up and down) though the tendency now is to downclock
more aggressively to compensate for the RPS boosts.

v2: Rebase
v3: Exclude Cherrytrail as Deepak was concerned that the increased
number of register writes would wake the common powerwell too often.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Deepak S <deepak.s@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: NDeepak S <deepak.s@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The logical place for clearing the RPS latched interrupt bits is when
resetting the RPS interrupts, so move the corresponding part from the RPS
disable function to the reset function. During resetting we already
cleared the IIR bits, so the only thing missing there was clearing pm_iir.

Note that we call gen6_disable_rps_interrupts() also during driver load
and resume time via intel_uncore_sanitize() when i915 interrupts are
still not installed. If there are any pending RPS bits at this point
(which after this patch wouldn't be cleared) they will be cleared by the
reset code via the interrupt preinstall hooks.
Signed-off-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

When disabling RPS interrupts there is a race where we disable RPS
inerrupts while the interrupt handler is running and the handler has
already latched the pending RPS interrupt from the master IIR register.
Afterwards the disabling path clears the PM IIR bits, making the state
of pending interrupts inconsistent from the interrupt handler's point of
view. This triggers the following warning: "The master control interrupt
lied (PM)!".

To fix this make sure that any running interrupt handler (which may
have already latched the master IIR) finishes before clearing the IIR
bits.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=87347Signed-off-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Use both up/down manual ei calcuations for symmetry and greater
flexibility for reclocking, instead of faking the down interrupt based
on a fixed integer number of up interrupts.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Deepak S<deepak.s@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Rewrite commit 31685c25
Author: Deepak S <deepak.s@linux.intel.com>
Date:   Thu Jul 3 17:33:01 2014 -0400

    drm/i915/vlv: WA for Turbo and RC6 to work together.

Other than code clarity, the major improvement is to disable the extra
interrupts generated when idle.  However, the reclocking remains rather
slow under the new manual regime, in particular it fails to downclock as
quickly as desired. The second major improvement is that for certain
workloads, like games, we need to combine render+media activity counters
as the work of displaying the frame is split across the engines and both
need to be taken into account when deciding the global GPU frequency as
memory cycles are shared.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Deepak S <deepak.s@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Deepak S<deepak.s@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Earlier Turbo interrupts were not being processed for SKL,
as something was amiss in turbo programming for SKL.
Now missing changes have been added, so enabling the Turbo
interrupt processing for SKL.
Signed-off-by: NAkash Goel <akash.goel@intel.com>
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The pipe interrupt registers are in the actual pipe power well, so we
need to restore them when re-enable the corresponding power well.

I've also copied what we do on HSW/BDW for VGA, even if the we haven't
enabled unclaimed registers just yet.

v2: Don't run skl_power_well_post_enable() if the power well is already
    enabled (Paulo)
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

While we only need to restore pipe B/C interrupt registers on BDW when
enabling the power well, skylake a bit more flexible and we'll also need
to restore the pipe A registers as it has its own power well that can be
toggled.
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

As vendors transition their drivers from legacy to atomic there's some
duplication of data between drm_crtc and drm_crtc_state (since
unconverted drivers likely won't have a state structure).

i915 is partially converted and does have a crtc->state structure, but
still uses direct crtc fields internally in many places, which causes
the two sets of data to get out of sync.  As of commit

        commit 31c946e8
        Author: Daniel Vetter <daniel.vetter@ffwll.ch>
        Date:   Sun Feb 22 12:24:17 2015 +0100

            drm: If available use atomic state in getcrtc ioctl

            This way drivers fully converted to atomic don't need to update these
            legacy state variables in their modeset code any more.
Reviewed-by: NRob Clark <robdclark@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>

the DRM core starts assuming that the presence of a ->state structure
implies that it should make use of the values stored there which, on
i915, leads to the core code using stale values for CRTC 'enabled'
status.

Let's switch over to using the state value of 'enable' internally rather
than using the drm_crtc field.  This ensures that our driver internals
are working from the same data that the DRM core is, avoiding
mismatches.

This patch was generated with Coccinelle using the following semantic
patch:

        <smpl>
        @@
        struct drm_crtc C;
        struct drm_crtc *CP;
        @@
        (
        - C.enabled
        + C.state->enable
        |
        - CP->enabled
        + CP->state->enable
        )

        // For assignments, we still update the legacy value as well as the state value
        // so add an extra assignment statement for that.
        @@
        struct drm_crtc C;
        struct drm_crtc *CP;
        expression E;
        @@
        (
          C.state->enable = E;
        + C.enabled = E;
        |
          CP->state->enable = E;
        + CP->enabled = E;
        )
        </smpl>

The crtc->mode and crtc->hwmode fields should probably be transitioned
over as well eventually, but we seem to do an okay job of keeping those
up-to-date already so I want to minimize the changes that will clash
with Ander's in-progress atomic work.

v2: Don't remove the assignments to the legacy value when we assign to
    the state value.  A second cocci stanza takes care of adding the
    legacy assignment back where appropriate.  (Daniel)

Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: NMatt Roper <matthew.d.roper@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Atm, it's possible that the interrupt handler is called when the device
is in D3 or some other low-power state. It can be due to another device
that is still in D0 state and shares the interrupt line with i915, or on
some platforms there could be spurious interrupts even without sharing
the interrupt line. The latter case was reported by Klaus Ethgen using a
Lenovo x61p machine (gen 4). He noticed this issue via a system
suspend/resume hang and bisected it to the following commit:

commit e11aa362
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Wed Jun 18 09:52:55 2014 -0700

    drm/i915: use runtime irq suspend/resume in freeze/thaw

This is a problem, since in low-power states IIR will always read
0xffffffff resulting in an endless IRQ servicing loop.

Fix this by handling interrupts only when the driver explicitly enables
them and so it's guaranteed that the interrupt registers return a valid
value.

Note that this issue existed even before the above commit, since during
runtime suspend/resume we never unregistered the handler.

v2:
- clarify the purpose of smp_mb() vs. synchronize_irq() in the
  code comment (Chris)

v3:
- no need for an explicit smp_mb(), we can assume that synchronize_irq()
  and the mmio read/writes in the install hooks provide for this (Daniel)
- remove code comment as the remaining synchronize_irq() is self
  explanatory (Daniel)

v4:
- drm_irq_uninstall() implies synchronize_irq(), so no need to call it
  explicitly (Daniel)

Reference: https://lkml.org/lkml/2015/2/11/205Reported-and-bisected-by: NKlaus Ethgen <Klaus@Ethgen.ch>
Cc: stable@vger.kernel.org
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

UMS is no more!

Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>