Check that there was not a late recovery between us declaring the GPU
hung and processing the reset. If the GPU did recover by itself, let the
request remain on the active list and see if it hangs again!
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161004201132.21801-5-chris@chris-wilson.co.uk

Whilst we reset the GPU, we want to prevent execlists from submitting
new work (which it does via an interrupt handler). To achieve this we
disable the irq (and drain the irq tasklet) around the reset. When we
enable it again afters, the interrupt queue should be empty and we can
reinitialise from a known state without fear of the tasklet running
concurrently.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161004201132.21801-4-chris@chris-wilson.co.uk

After a GPU reset, we want to replay our queue of requests. However, the
GPU reset clobbered the state and we only fixup the state for the guilty
request - and engines deemed innocent we try to leave untouched so that
we recover as completely as possible. However, we need to clear the sw
tracking of the ELSP ports even for innocent requests, so move the clear
to the common path of init_hw (from reset_hw).
Reported-by: NMika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161004201132.21801-3-chris@chris-wilson.co.uk

On Braswell, at least, we observe that the context image is written in
multiple phases. The first phase is to clear the register state, and
subsequently rewrite it. A GPU reset at the right moment can interrupt
the context update leaving it corrupt, and our update of the RING_HEAD
is not sufficient to restart the engine afterwards. To recover, we need
to reset the registers back to their original values. The context state
is lost. What we need is a better mechanism to serialise the reset with
pending flushes from the GPU.

Fixes: 821ed7df ("drm/i915: Update reset path to fix incomplete requests")
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161004201132.21801-2-chris@chris-wilson.co.uk

Since both legacy and execlists want to populate the RING_CTL register,
share the computation of the right bits for the ring->size. We can then
stop masking errors and explicitly forbid them during creation!
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161004201132.21801-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_execbuffer.c:432:52: warning: incorrect type in argument 1 (different address spaces)
drivers/gpu/drm/i915/i915_gem_execbuffer.c:432:52:    expected void [noderef] <asn:2>*vaddr
drivers/gpu/drm/i915/i915_gem_execbuffer.c:432:52:    got void *
drivers/gpu/drm/i915/i915_gem_execbuffer.c:477:15: warning: incorrect type in assignment (different address spaces)
drivers/gpu/drm/i915/i915_gem_execbuffer.c:477:15:    expected void *vaddr
drivers/gpu/drm/i915/i915_gem_execbuffer.c:477:15:    got void [noderef] <asn:2>*

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475574853-4178-2-git-send-email-jani.nikula@intel.com

Fix sparse warning:

drivers/gpu/drm/i915/intel_pm.c:3970:1: warning: symbol
'skl_ddb_add_affected_planes' was not declared. Should it be static?

Fixes: 7f60e200 ("drm/i915/gen9: only add the planes actually affected by ddb changes")
Cc: Lyude <cpaul@redhat.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475573357-30562-1-git-send-email-jani.nikula@intel.com

Instead of using bsearch library function make a local generator
macro out of it so the comparison callback can be inlined.
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Suggested-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1475569769-31108-1-git-send-email-tvrtko.ursulin@linux.intel.com

Simply replace the linear search with the kernel's binary
search implementation. There is only six registers currently
in that table so this may not be that interesting. It adds a
function call so hopefully remains performance neutral for now.

v2: No need for manual conversion to bool for return.
    (Joonas Lahtinen)
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

Also verify the order at runtime. This was we can start using
binary search on it in a following patch.

v2: Add comment on the sorted array and only check it when
    debug option is enabled.

v3: Use IS_ENABLED. (Chris Wilson)
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> (v1)
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

We notice two identical copies of the shadow register table and
following from that removal can also unify CHV and Gen9 write
mmio functions and macros into a single implementation.

v2: Name fwtable consistently and use HAS_FWTABLE. (Joonas Lahtinen)
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

It is now obvious VLV, CHV and Gen9 mmio read fcuntions are
completely identical so we can remove the three copies and
just keep the newly named generic implementation.

v2: Use fwtable naming consistently. (Joonas Lahtinen)
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

Remove some macros which are now obviously identical.

v2: Added HAS_FWTABLE macro and simplified intel_uncore_forcewake_for_read.
    (Joonas Lahtinen)
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

If we store this in the uncore structure we are on a good way to
show more commonality between the per-platform implementations.

v2: Constify table pointer and correct coding style. (Chris Wilson)
v3: Rebase.
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

If we insert blitter forcewake domain entries in the range
table we can eliminate that special case and simplify the
code in a few macros. This will enable more unification later.
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

Instead of the existing linear seach, now that we have sorted
range tables, we can do a binary search on them for some
potential miniscule performance gain, but more importantly
for elegance and code size. Hopefully the perfomance gain is
sufficient to offset the function calls which were not there
before.

v2: Removed const cast away.
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

Sorting the tables (verified at runtime to help during
development) is another prerequisite for interesting
work which will follow.

v2:
 * Remove const away cast and improve comments. (Chris Wilson)
 * Check tables only when debug option is enabled.

v3: Use IS_ENABLED. (Chris Wilson)
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

Move finding the correct forcewake domains to take for
register access from code to a mapping table. This will
allow more interesting work in the following patches
and is easier to review if singled out early.
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

Once we know we need to take new forcewakes, that being
a slow operation, it does not make sense to inline that
code into every mmio accessor.

Move it to a separate function and save some code.

v2: Be explicit with noinline and remove stale comment.
    (Chris Wilson)
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

There are current places in the code, and there will be more in the
future, which iterate the forcewake domains to find out which ones
are currently active.

To save them from doing this iteration, we can cheaply keep a mask
of active domains in dev_priv->uncore.fw_domains_active.

This has no cost in terms of object size, even manages to shrink it
overall by 368 bytes on my config.
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: "Paneri, Praveen" <praveen.paneri@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

They are completely identical to gen6_write* ones.
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>

Fix sparse warning:

drivers/gpu/drm/i915/intel_device_info.c:195:31: warning: Variable
length array is used.

In truth the array does have constant length, but sparse is too dumb to
realize. This is a bit ugly, but silence the warning no matter what.

Fixes: 91bedd34 ("drm/i915/bdw: Check for slice, subslice and EU count for BDW")
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475574853-4178-1-git-send-email-jani.nikula@intel.com

Move the outcast intel_fbdev_output_poll_changed() stub for
CONFIG_DRM_FBDEV_EMULATION=n next to its friends.
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475567628-5529-1-git-send-email-jani.nikula@intel.com

When decoding the semaphores inside hangcheck, we need to use the hw-id
and not the local array index.

Fixes: de1add36 ("drm/i915: Decouple execbuf uAPI ...")
Testcase: igt/gem_exec_whisper/hang # gen6-7
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161003124516.12388-3-chris@chris-wilson.co.uk

We use obj->phys_handle to choose the pread/pwrite path, but as
obj->phys_handle is a union with obj->userptr, we then mistakenly use
the phys_handle path for userptr objects within pread/pwrite.

Testcase: igt/gem_userptr_blits/forbidden-operations
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97519Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161003124516.12388-2-chris@chris-wilson.co.uk

When we enable the per-register access mmiodebug, it is to detect which
access is illegal. Reporting on earlier untraced access outside of the
mmiodebug does not help debugging (as the suspicion is immediately put
upon the current register which is not at fault)!

References: https://bugs.freedesktop.org/show_bug.cgi?id=97985Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Cc: stable@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/20161003124516.12388-1-chris@chris-wilson.co.uk

We were previously adding all the planes owned by the CRTC even when
the ddb partitioning didn't change for them. As a consequence, a lot
of functions were being called when we were just moving the cursor
around the screen, such as skylake_update_primary_plane().

This was causing flickering on the primary plane when moving the
cursor. I'm not 100% sure which operation caused the flickering, but
we were writing to a lot of registers, so it could be any of these
writes. With this patch, just moving the mouse won't add the primary
plane to the commit since it won't trigger a change in DDB
partitioning.

v2: Use skl_ddb_entry_equal() (Lyude).
v3: Change Reported-and-bisected-by: to Reported-by: for checkpatch

Fixes: 05a76d3d ("drm/i915/skl: Ensure pipes with changed wms get added to the state")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97888
Cc: Mike Lothian <mike@fireburn.co.uk>
Cc: stable@vger.kernel.org
Reported-by: NMike Lothian <mike@fireburn.co.uk>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NLyude <cpaul@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475177808-29955-1-git-send-email-paulo.r.zanoni@intel.com

This reverts 'commit 3708d5e0 ("drm/i915: start adding dp mst audio")'
because it breaks MST multi-monitor setups on some platforms.

Fixes: 3708d5e0 ("drm/i915: start adding dp mst audio")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97907Signed-off-by: NDhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reported-by: NKim Lidström <kim@dxtr.im>
Cc: Libin Yang <libin.yang@linux.intel.com>
Cc: Lyude <cpaul@redhat.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475132104-2754-1-git-send-email-dhinakaran.pandiyan@intel.com

DPLL_SDVO_HIGH_SPEED must be set for SDVO/HDMI/DP, but nowhere is it
forbidden to set it for LVDS/CRT as well. So let's also set it on
CRT to make it possible to share the DPLL between HDMI and CRT.

What that bit apparently does is enable the x5 clock to the port,
which then pumps out the bits on both edges of the clock. The DAC
doesn't need that clock since it's not pumping out bits, but I don't
think it hurts to have the DPLL output that clock anyway.

This is fairly important on IVB since it has only two DPLLs with three
pipes. So trying to drive three or more PCH ports with three pipes
is only possible when at least one of the DPLLs gets shared between
two of the pipes.

SNB doesn't really need to do this since it has only two pipes. It could
be done to avoid enabling the second DPLL at all in certain cases, but
I'm not sure that's such a huge win. So let's not do it for SNB, at
least for now. On ILK it never makes sense as the DPLLs can't be shared.

v2: Just always enable the high speed clock to keep things simple (Daniel)
    Beef up the commit message a bit (Daniel)

Cc: Nick Yamane <nick.diego@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Tested-by: NNick Yamane <nick.diego@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97204Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474878646-17711-1-git-send-email-ville.syrjala@linux.intel.comReviewed-by: NAnder Conselvan de Oliveira <conselvan2@gmail.com>

Replace dev with dev_priv and INTEL_INFO with INTEL_GEN

v1:
* Rebased on drm-nightly (Jani Nikula)
* Separated from the link training patch series
Signed-off-by: NManasi Navare <manasi.d.navare@intel.com>
Reviewed-by: NMika Kahola <mika.kahola@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475019413-19811-1-git-send-email-manasi.d.navare@intel.com

a277ca7d should've been a no-functional-change commit, but it
removed the initialization of the dpll_hw_state for HDMI outputs,
resulting in state mismatches and a failed modeset with blank
screen. Fix this by reinstating the dpll_hw_state initialization.

v2:
- Make bxt_ddi_hdmi_set_dpll_hw_state() static.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Cc: Durgadoss R <durgadoss.r@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Fixes: a277ca7d ("drm/i915: Split bxt_ddi_pll_select()")
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NAnder Conselvan de Oliveira <conselvan2@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474901671-22719-1-git-send-email-imre.deak@intel.com

We just removed the implementation for all the pre-production
workarounds, so now tell the user that we expect his machine to not
work properly. Also convert this to DRM_ERROR so we can more easily
spot these problems in bug reports and CI/QA runs.

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474891672-23414-2-git-send-email-jani.nikula@intel.com

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474891672-23414-1-git-send-email-jani.nikula@intel.com

When i915_fbc_status is read while fbc is disabled,
it reports compressing to be true, which is confusing.
Report compressing only when fbc is enabled.

v2 (from Paulo): commit message capitalization.
Signed-off-by: Nvathsala nagaraju <vathsala.nagaraju@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474534193-9527-1-git-send-email-vathsala.nagaraju@intel.com

Now that this code is part of the compute stage we can return -EINVAL
to prevent the modeset instead of giving a WARN and trying anyway.

v2:
 - Fix typo (Paul Menzel).
 - Add MISSING_CASE() (Ville, Maarten).
Reported-by: NLyude <cpaul@redhat.com>
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474578035-424-10-git-send-email-paulo.r.zanoni@intel.com

This should affect linear and X tiled planes on really small htotal
cases. It doesn't seem to be a very feasible case, but let's implement
it since it's on the specification and it's better to have it and
never need than not have it and realize we needed it.
Reviewed-by: NLyude <cpaul@redhat.com>
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474578035-424-9-git-send-email-paulo.r.zanoni@intel.com

We forgot the "res_blocks += y_tile_minimum" that's described on step
V of our documentation.

Again, this should only affect the Y tiling cases.

It looks like the relevant code was introduced in 0fda6568, but
there's always the possibility that it matched our specification when
it was introduced, and then the specification changed while the code
stayed the same. So we can't really say this was a regression, but
let's try to add a "Fixes" tag anyway to help backporting.

v2: Try to add a "Fixes" tag (Maarten).

Fixes: 0fda6568 ("drm/i915/skl: Update watermarks for Y tiling")
Cc: stable@vger.kernel.org
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NLyude <cpaul@redhat.com>
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474578035-424-8-git-send-email-paulo.r.zanoni@intel.com

The confusing thing is that plane_blocks_per_line is listed as part of
the method 2 calculation but is also used for other things. We
calculated it in two different places and different ways: one inside
skl_wm_method2() and the other inside skl_compute_plane_wm(). The
skl_wm_method2() implementation is the one that matches the
specification.

With this patch we fix the skl_compute_plane_wm() calculation and just
pass it as a parameter to skl_wm_method2(). We also take care to not
modify the value of plane_bytes_per_line since we're going to rely on
it having a correct value in later patches.

This should affect the watermarks for Linear and Y-tiled.

From my analysis, it looks like the two plane_blocks_per_line
variables got out of sync on 0fda6568, but we can't really say
that commit was a regression, it looks like just an incomplete fix.
There's always the possibility that 0fda6568 matched our
specification at that time, and then later the specification changed.

v2: Try to add a "Fixes" tag (Maarten).

Fixes: 0fda6568 ("drm/i915/skl: Update watermarks for Y tiling")
Cc: stable@vger.kernel.org
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NLyude <cpaul@redhat.com>
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474578035-424-7-git-send-email-paulo.r.zanoni@intel.com

During watermarks calculations, this value is used in 3 different
places. Only one of them was not using a hardcoded 4. Move the code up
so everybody can benefit from the actual value.

This should only help on situations with Y tiling + 90/270 rotation +
1 or 2 bpp or NV12.

Cc: stable@vger.kernel.org
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474578035-424-6-git-send-email-paulo.r.zanoni@intel.com

Bspec says:
  "The mailbox response data may not account for memory read latency.
   If the mailbox response data for level 0 is 0us, add 2 microseconds
   to the result for each valid level."

This means we should only do the +2 in case wm[0] == 0, not always.

So split the sanitizing implementation from the WA implementation and
fix the WA implementation.

v2: Add Fixes tag (Maarten).

Fixes: 367294be ("drm/i915/gen9: Add 2us read latency to WM level")
Cc: stable@vger.kernel.org
Cc: Vandana Kannan <vandana.kannan@intel.com>
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474578035-424-5-git-send-email-paulo.r.zanoni@intel.com