Cc: Thierry Reding <thierry.reding@avionic-design.de>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Acked-by: NDave Airlie <airlied@gmail.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

In some places, we want to know if an object is bound in any address
space, and not just the global GTT. This often applies when there is a
single global resource (object, pages, etc.)

function                             |      reason
--------------------------------------------------
i915_gem_object_is_inactive          | global object
i915_gem_object_put_pages            | object's pages
915_gem_object_unpin                 | global object
i915_gem_execbuffer_unreserve_object | temporary until we plumb vma
pread/pwrite                         | see the note below

Note: set_to_gtt_domain in pwrite/pread is abused as a wait_rendering
call - but that once only worked if the object is bound. We really
should replace this with a plain wait_rendering call, which would have
the upside that in pread it would be clearer that we actually only
wait for oustanding gpu writes.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
[danvet: Explain the set_to_gtt_domain in pwrite/pread and volunteer
Ben to replace those with wait_rendering calls.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Eviction code, like the rest of the converted code needs to be aware of
the address space for which it is evicting (or the everything case, all
addresses). With the updated bind/unbind interfaces of the last patch,
we can now safely move the eviction code over.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

As alluded to in several patches, and it will be reiterated later... A
VMA is an abstraction for a GEM BO bound into an address space.
Therefore it stands to reason, that the existing bind, and unbind are
the ones which will be the most impacted. This patch implements this,
and updates all callers which weren't already updated in the series
(because it was too messy).

This patch represents the bulk of an earlier, larger patch. I've pulled
out a bunch of things by the request of Daniel. The history is preserved
for posterity with the email convention of ">" One big change from the
original patch aside from a bunch of cropping is I've created an
i915_vma_unbind() function. That is because we always have the VMA
anyway, and doing an extra lookup is useful. There is a caveat, we
retain an i915_gem_object_ggtt_unbind, for the global cases which might
not talk in VMAs.

> drm/i915: plumb VM into object operations
>
> This patch was formerly known as:
> "drm/i915: Create VMAs (part 3) - plumbing"
>
> This patch adds a VM argument, bind/unbind, and the object
> offset/size/color getters/setters. It preserves the old ggtt helper
> functions because things still need, and will continue to need them.
>
> Some code will still need to be ported over after this.
>
> v2: Fix purge to pick an object and unbind all vmas
> This was doable because of the global bound list change.
>
> v3: With the commit to actually pin/unpin pages in place, there is no
> longer a need to check if unbind succeeded before calling put_pages().
> Make put_pages only BUG() after checking pin count.
>
> v4: Rebased on top of the new hangcheck work by Mika
> plumbed eb_destroy also
> Many checkpatch related fixes
>
> v5: Very large rebase
>
> v6:
> Change BUG_ON to WARN_ON (Daniel)
> Rename vm to ggtt in preallocate stolen, since it is always ggtt when
> dealing with stolen memory. (Daniel)
> list_for_each will short-circuit already (Daniel)
> remove superflous space (Daniel)
> Use per object list of vmas (Daniel)
> Make obj_bound_any() use obj_bound for each vm (Ben)
> s/bind_to_gtt/bind_to_vm/ (Ben)
>
> Fixed up the inactive shrinker. As Daniel noticed the code could
> potentially count the same object multiple times. While it's not
> possible in the current case, since 1 object can only ever be bound into
> 1 address space thus far - we may as well try to get something more
> future proof in place now. With a prep patch before this to switch over
> to using the bound list + inactive check, we're now able to carry that
> forward for every address space an object is bound into.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
[danvet: Rebase on top of the loss of "drm/i915: Cleanup more of VMA
in destroy".]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

In order to do this for all VMs, it's convenient to rework the logic a
bit. This should have no functional impact.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Rather than open-code the teardown of a framebuffer, export the routine
from intel_display.c. This then make intel_fbdev symmetric in its use of
the common intel_framebuffer routines to initialise and clean up the
struct intel_framebuffer. (And new features need only be added in one
location!)
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

MLC_LLC was never validated for Sandybridge and was superseded by a new
level of cacheing for the GPU in Ivybridge. Update our names to be
consistent with usage, and in the process stop setting the unwanted bit
on Sandybridge.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
[danvet: s/BUG/WARN_ON(1) bikeshed.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

We set the mode based on the port, and we already pass the port as an
argument.
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

These messages are not really useful since it's very easy to check
which mode is used for each port: The values programmed are based on
the port type, then assigned to the ddi_translations variable.
Currently we use DP mode for ports A-D and FDI mode for port E.

Also, when we add the code to enable/disable PC8+,
intel_prepare_ddi_buffers will be called more often and will eat your
dmesg buffers.

While at it, fix the coding style of the "for" statement above.
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Pimp commit message with Paulo's more detailed explanation of
how the ddi translation buffer settings are computed, to answer a
question from Chris.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The code itself is no longer accurate without updating once we have
multiple address space since clearing the domains of every object
requires scanning the inactive list for all VMs.

"This code is dead. Just remove it rather than port it to vma." - Chris
Wilson
Recommended-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NBen Widawsky <benjamin.widawsky@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

All the ILK+ WM compute functions take the latency values in 0.1us
units. Add a few comments to remind people about that.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Adjust the current ILK/SNB/IVB watermark codepaths to use the
pre-populated latency values from dev_priv instead of reading
them out from the registers every time.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Return UINT_MAX for the calculated WM level if the latency is zero.
This will lead to marking the WM level as disabled.

I'm not sure if latency==0 should mean that we want to disable the
level. But that's the implication I got from the fact that we don't
even enable the watermark code of the SSKDP register is 0.

v2: Use WARN() to scare people
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Seeing the watermark latency values in dmesg might help sometimes.

v2: Use DRM_ERROR() when expected latency values are missing

Note: We might hit the DRM_ERROR added in this patch and apparently
there's not much we can do about that. But I think it'd be interesting
to figure out whether that actually happens in the real world, so I
didn't apply a s/DRM_ERROR/DRM_DEBUG_KMS/ bikeshed while applying.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Add note about new error dmesg output.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Rather than pass around the plane latencies, just grab them from
dev_priv nearer to where they're needed. Do the same for cursor
latencies.

v2: Add some comments about latency units
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Rather than having to read the latency values out every time, just
store them in dev_priv.

On ILK and IVB there is a difference between some of the latency
values for different planes, so store the latency values for each
plane type separately, and apply the necesary fixups during init.

v2: Fix some checkpatch complaints
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

ILK has a slightly different way to read out the watermark
latency values. On ILK the LP0 latenciy values are in fact
not stored in any register, and instead we must use fixed
values.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Hangcheck, and some of the recent reset code for guilty batches need to
know which address space the object was in at the time of a hangcheck.
This is because we use offsets in the (PP|G)GTT to determine this
information, and those offsets can differ depending on which VM they are
bound into.

Since we still only have 1 VM ever, this code shouldn't yet have any
impact.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

With multiple VMs, the eviction code benefits from being able to blindly
put pages without needing to know if there are any entities still
holding on to those pages. As such it's preferable to return the -EBUSY
before the BUG.

Eviction code is the only user for now, but overall it makes sense
anyway, IMO.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

For now, objects will maintain the same cache levels amongst all address
spaces. This is to limit the risk of bugs, as playing with cacheability
in the different domains can be very error prone.

In the future, it may be optimal to allow setting domains per VMA (ie.
an object bound into an address space).
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

This represents the first half of hooking up VMs to execbuf. Here we
basically pass an address space all around to the different internal
functions. It should be much more readable, and have less risk than the
second half, which begins switching over to using VMAs instead of an
obj,vm.

The overall series echoes this style of, "add a VM, then make it smart
later"
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
[danvet: Switch a BUG_ON to WARN_ON.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Make it aware of which domain it is bound into GGTT, or PPGTT.

While modifying the function, add a global gtt flag to the object
description. Global is more interesting than aliasing since aliasing is
the default.

v2: Access VMA directly for start/size instead of helpers (Daniel)
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Just some small cleanups, and a rename of vm->ggtt_vm requested by
Daniel.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

To verbalize it, one can say, "pin an object into the given address
space." The semantics of pinning remain the same otherwise.

Certain objects will always have to be bound into the global GTT.
Therefore, global GTT is a special case, and keep a special interface
around for it (i915_gem_obj_ggtt_pin).

v2: s/i915_gem_ggtt_pin/i915_gem_obj_ggtt_pin
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Do to the move active/inactive lists, it no longer makes sense to use
them for shrinking, since shrinking isn't VM specific (such a need may
also exist, but doesn't yet).

What we can do instead is use the global bound list to find all objects
which aren't active.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Earlier in the conversion sequence we attempted to quickly wedge in the
transitional interface as static inlines.

Now that we're sure these interfaces are sane, for easier debug and to
decrease code size (since many of these functions may be called quite a
bit), make them real functions

While at it, kill off the set_color interface. We'll always have the
VMA, or easily get to it.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

With an upcoming change to bind, to make checkpatch happy and keep the
code clean, we need to rework this code a bit.

This should have no functional impact.
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
[danvet: Add the newline Chris requested.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Move all the similar address space (VM) initialization code to one
function. Until we have multiple VMs, there should only ever be 1 VM.
The aliasing ppgtt is a special case without it's own VM (since it
doesn't need it's own address space management).
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The default LLC age was changed:
commit 0d8ff15e
Author: Ben Widawsky <benjamin.widawsky@intel.com>
Date:   Thu Jul 4 11:02:03 2013 -0700

drm/i915/hsw: Set correct Haswell PTE encodings.

On the surface it would seem setting a default age wouldn't matter
because all GEM BOs are aged similarly, so the order in which objects
are evicted would not be subject to aging. The current working theory as
to why this caused a regression though is that LLC is a bit special in
that it is shared with the CPU. Presumably (not verified) the CPU
fetches cachelines with age 3, and therefore recently cached GPU objects
would be evicted before similar CPU object first when the LLC is full.
It stands to reason therefore that this would negatively impact CPU
bound benchmarks - but those seem to be low on the priority list.

eLLC OTOH does not have this same property as LLC. It should be used
entirely for the GPU, and so the age really shouldn't matter.
Furthermore, we have no evidence to suggest one is better than another
on eLLC. Since we've never properly supported eLLC before no, there
should be no regression. If the GPU client really wants "younger"
objects, they should use MOCS.

v2: Drop the extra #define (Chad)

v3: Actually git add

v4: Pimped commit message

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67062Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Reviewed-by: NChad Versace <chad.versace@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Since commit 29a241cc (ACPICA: Add argument typechecking for all
predefined ACPI names), _DSM parameters are validated which trigger the
following warning:

    ACPI Warning: \_SB_.PCI0.GFX0._DSM: Argument #4 type mismatch - Found [Integer], ACPI requires [Package] (20130517/nsarguments-95)
    ACPI Warning: \_SB_.PCI0.GFX0._DSM: Argument #4 type mismatch - Found [Integer], ACPI requires [Package] (20130517/nsarguments-95)
    ACPI Warning: \_SB_.PCI0.P0P2.PEGP._DSM: Argument #4 type mismatch - Found [Integer], ACPI requires [Package] (20130517/nsarguments-95)
    ACPI Warning: \_SB_.PCI0.P0P2.PEGP._DSM: Argument #4 type mismatch - Found [Integer], ACPI requires [Package] (20130517/nsarguments-95)

As the Intel _DSM method seems to ignore this parameter, let's comply to
the ACPI spec and use a Package instead.
Signed-off-by: NPeter Wu <lekensteyn@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=32602Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Userspace can pass a mode with an unspecified vsync/hsync polarity
setting. All encoders in the Intel driver take this to mean a negative
polarity setting. The HW readout/state checker code on the other hand
needs these flags to be explicitly set, otherwise the state checker will
WARN about the mismatch.

Get rid of the WARN by making the polarity setting explicit in the
adjusted mode flags based on the requested mode flags. This will keep
the existing behavior otherwise.

Note that we could guess from the other timing parameters whether the
user wanted a VESA or other standard mode and set the polarity
accordingly. This is what the NV driver does
(drivers/gpu/drm/nouveau/dispnv04/crtc.c), but I think that's not very
exact and would change the existing behavior of the Intel driver.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65442Signed-off-by: NImre Deak <imre.deak@intel.com>
Tested-by: Ncancan,feng <cancan.feng@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

VLV wants encoder enabling before the pipe is up. With the previously
rearranged VLV DP and HDMI ->pre_enable and ->enable callbacks in place,
this no longer depends on the early ->enable hook call. Move the
->enable call at the end of the sequence, similar to the crtc enable on
other platforms. This will be needed e.g. for moving the eDP backlight
enabling to the right place in the sequence, currently done too early on
VLV.

There should be no functional changes.

v2: Rebase.

v3: Explain why this is needed in the commit message (Chris).
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

VLV wants encoder enabling before the pipe is up. This is currently
achieved through calling the ->enable callback early, right after the
->pre_enable callback, in valleyview_crtc_enable(). This loses both the
distinction between ->pre_enable and ->enable on VLV and the possibility
to use a hook at the end of the modeset sequence.

Rearrange the HDMI callbacks to make it possible to move ->enable call
later. Basically do everything in ->pre_enable on VLV, and make ->enable
a NOP.

There should be no functional changes.

v2: Rebase.

v3: Explain why this is needed in the commit message (Chris).
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

VLV wants encoder enabling before the pipe is up. This is currently
achieved through calling the ->enable callback early, right after the
->pre_enable callback, in valleyview_crtc_enable(). This loses both the
distinction between ->pre_enable and ->enable on VLV and the possibility
to use a hook at the end of the modeset sequence.

Rearrange the DP callbacks to make it possible to move ->enable call
later. Basically do everything in ->pre_enable on VLV, and make ->enable
a NOP.

There should be no functional changes.

v2: Rebase.

v3: Explain why this is needed in the commit message (Chris).
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Otherwise we get flooded by the kernel warning us that we are doing
long sequences of IO without serialisation. For example,

 WARNING: CPU: 0 PID: 11136 at drivers/gpu/drm/i915/intel_sideband.c:40 vlv_sideband_rw+0x48/0x1ef()
 Modules linked in:
 CPU: 0 PID: 11136 Comm: kworker/u2:0 Tainted: G        W    3.11.0-rc2+ #4
 Call Trace:
  [<c2028564>] ?  warn_slowpath_common+0x63/0x78
  [<c227ad43>] ?  vlv_sideband_rw+0x48/0x1ef
  [<c20285dd>] ?  warn_slowpath_null+0xf/0x13
  [<c227ad43>] ?  vlv_sideband_rw+0x48/0x1ef
  [<c227b060>] ?  vlv_dpio_write+0x1c/0x21
  [<c2262b3b>] ?  intel_dp_set_signal_levels+0x24a/0x385
  [<c2264909>] ?  intel_dp_complete_link_train+0x25/0x1d1
  [<c2264c55>] ?  intel_dp_check_link_status+0xf7/0x106
  [<c2238ced>] ?  i915_hotplug_work_func+0x17b/0x221
  [<c203a204>] ?  process_one_work+0x12e/0x210
  [<c203a5e4>] ?  worker_thread+0x116/0x1ad
  [<c203a4ce>] ?  rescuer_thread+0x1cb/0x1cb
  [<c203d8f5>] ?  kthread+0x67/0x6c
  [<c2457ebb>] ?  ret_from_kernel_thread+0x1b/0x30
  [<c203d88e>] ?  init_completion+0x18/0x18

v2: Retire the locking in vlv_crtc_enable() and do it close to the meat.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
[danvet: Squash in a s/mutex_lock/mutex_unlock/ fixup spotted by the 0
day kernel build/coccinelle and reported by Dan Carpenter.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Art confirms that this should work fine.  Since most panels are 18bpp
with dithering from 24bpp, the existing code wouldn't be enabled in most
cases.
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

SNB and IVB have slightly a different way to read out the
watermark latency values.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

The LP1+ watermark latency values need to be multiplied by 5 to
make them suitable for watermark calculations. However on pre-HSW
platforms we're going to need the raw value later when we have to
write it to the WM_LPn registers' latency field. So delay the
multiplication until it's needed.

Note: Paulo complains that the units of wm (now in 100ns) aren't
really clear and I agree. But that can be fixed later on ...
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Add a comment about the unit obfuscation.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Move parsing of MCH_SSKPD to a separate function, we'll add other
platforms there later.

Note: Chris spotted an empty struct initializer and wondered whether
that is hiding a compilier warning. Ville explained that it should
have been part of the patch that extends this function to snb/ivb,
which don't have all levels hsw has. I've figured it's ok to keep it
here with a small note.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Add note about the ominous struct initializer.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>