To get context hang statistics for specified context,
add i915_gem_context_get_hang_stats().
For arb-robustness, every context needs to have its own
hang statistics tracking. Added function will return
the user specified context statistics or in case of
default context, statistics from drm_i915_file_private.
v2: handle default context inside get_reset_state
v3: return struct pointer instead of passing it in as param
(Chris Wilson)
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Add some debug messages to help figure out what goes wrong on context
initialization.
Later in the PPGTT series, I ended up having a lot of failures after
reset. In many cases it was extra difficult to debug because I hadn't
even realized that contexts failed to reinitialize after reset (again an
artifact of some later patches).
This fairly benign patch does help debug some potential issues which
arise later.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
We did not mention the workaround name when implementing those. This
should help us track what we already implement.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Because our context refcounting doesn't grab a ref at lookup time, it is
unsafe to do so without the lock.
NOTE: We don't have an easy way to put the assertion in the lookup
function which is where this really belongs. Context switching is good
enough because it actually asserts even more correctness by protecting
the default_context.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: s/BUG/WARN/]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
In order to be notified of when the context and all of its associated
objects is idle (for if the context maps to a ppgtt) we need a callback
from the retire handler. We can arrange this by using the kref_get/put
of the context for request tracking and by inserting a request to
demarque the switch away from the old context.
[Ben: fixed minor error to patch compile, AND s/last_context/from/]
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Before module unload is called, gpu_idle() will switch
to default context. This will increment ref count of base
object as the default context is 'running' on module unload
time. Unreference the drm object so that when context
is freed, base object is freed as well.
v2: added comment to explain the refcounts (Ben Widawsky)
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Enabling PPGTT and also the need to track which context was guilty of
gpu hang (arb robustness enabling) have put pressure for struct i915_hw_context
to be more than just a placeholder for hw context state.
In order to track object lifetime properly in a multi peer usage, add reference
counting for i915_hw_context.
v2: track i915_hw_context pointers instead of using ctx_ids
(from Chris Wilson)
v3 (Ben): Get rid of do_release() and handle refcounting more compactly.
(recommended by Chis)
v4: kref_* put inside static inlines (Daniel Vetter)
remove code duplication on freeing context (Chris Wilson)
v5: idr_remove and ctx->file_priv = NULL in destroy ioctl (Chris)
This actually will cause a problem if one destroys a context and later
refers to the idea of the context (multiple contexts may have the same
id, but only 1 will exist in the idr).
v6: Strip out the request related stuff. Reworded commit message.
Got rid of do_destroy and introduced i915_gem_context_release_handle,
suggested by Chris Wilson.
v7: idr_remove can't be called inside idr_for_each (Chris Wilson)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net> (v5)
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com> (v7)
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Squash sob lines, the patch ping-ponged between Ben and Mika
a bit ...]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Enabling context support increases SwapBuffers latency by about 20%
(measured on an i7-3720qm). We can offset that loss slightly by enabling
faster caching for the contexts. As they are not backed by any
particular cache (such as the sampler or render caches) our only option
is to select the generic mid-level cache. This reduces the latency of
the swap by about 5%.
Oddly this effect can be observed running smokin-guns on IVB at
1280x1024:
Using BLT copies for swaps: 151.67 fps
Using Render copies for swaps (unpatched): 141.70 fps
With contexts disabled: 150.23 fps
With contexts in L3$: 150.77 fps
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Convert to the much saner new idr interface.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: David Airlie <airlied@linux.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
It's not that the assertion is incorrect, but rather that we can call
do_destroy early in loading, and we will falsely BUG().
Since contexts have been in for a while now, and in the internal APIs
are pretty stable, it should be fairly safe to remove this.
v2: Remove unused dev_priv, and dev
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This was a rebase error from when the patches originally landed. Since
the context size is unsigned, there is also no use in checking if it's
less than 0.
The existing code is not really wrong, but it's not simple as it should
be.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Based on the work by Mika Kuoppala, we realised that we need to handle
seqno wraparound prior to committing our changes to the ring. The most
obvious point then is to grab the seqno inside intel_ring_begin(), and
then to reuse that seqno for all ring operations until the next request.
As intel_ring_begin() can fail, the callers must already be prepared to
handle such failure and so we can safely add further checks.
This patch looks like it should be split up into the interface
changes and the tweaks to move seqno wrapping from the execbuffer into
the core seqno increment. However, I found no easy way to break it into
incremental steps without introducing further broken behaviour.
v2: Mika found a silly mistake and a subtle error in the existing code;
inside i915_gem_retire_requests() we were resetting the sync_seqno of
the target ring based on the seqno from this ring - which are only
related by the order of their allocation, not retirement. Hence we were
applying the optimisation that the rings were synchronised too early,
fortunately the only real casualty there is the handling of seqno
wrapping.
v3: Do not forget to reset the sync_seqno upon module reinitialisation,
ala resume.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=863861
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> [v2]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Whoops. This was fixed previously, but not sure how it got lost. It's
not needed for -fixes or stable because at the moment
drm_i915_file_private is way bigger than i915_hw_context (by 120 bytes
on my 64b build).
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Daniel writes:
Bigger -fixes pile, mostly because I've included Ajax' DP dongle stuff,
as discussed on irc. Otherwise just small things:
- regression fix to finally make 6bpc auto-dither on dp work (Jani)
- reinstate an snb ctx w/a that accidentally got lost in a rework (Chris)
- fixup the DP train sequence, logic-goof-up uncovered by Coverty (Chris)
- fix set_caching locking (Ben)
- fix spurious segfault on con-current gtt mmap faulting (Dimitry and Mika)
- some pageflip correctness fixes (still hunting down some issues, but
these are the worst offenders of confused code that we've tracked down
thus far) from Chris and me
- fixup swizzling settings on vlv (Jesse)
- gt_mode w/a from Ben added, fixes snb gt1 rc6+hw ctx hangs.
* 'drm-intel-fixes' of git://people.freedesktop.org/~danvet/drm-intel:
drm/i915: Fix GT_MODE default value
drm/i915: don't frob the vblank ts in finish_page_flip
drm/i915: call drm_handle_vblank before finish_page_flip
drm/i915: print warning if vmi915_gem_fault error is not handled
drm/i915: EBUSY status handling added to i915_gem_fault().
drm/i915: Try harder to complete DP training pattern 1
drm/i915: set swizzling to none on VLV
drm/dp: Make sink count DP 1.2 aware
drm/dp: Document DP spec versions for various DPCD registers
drm/i915/dp: Be smarter about connection sense for branch devices
drm/i915/dp: Fetch downstream port info if needed during DPCD fetch
drm/dp: Update DPCD defines
drm: Export drm_probe_ddc()
drm/i915: Flush the pending flips on the CRTC before modification
drm/i915: Actually invalidate the TLB for the SandyBridge HW contexts w/a
drm/i915: Fix set_caching locking
drm/i915: use adjusted_mode instead of mode for checking the 6bpc force flag
Pull drm merge (part 1) from Dave Airlie:
"So first of all my tree and uapi stuff has a conflict mess, its my
fault as the nouveau stuff didn't hit -next as were trying to rebase
regressions out of it before we merged.
Highlights:
- SH mobile modesetting driver and associated helpers
- some DRM core documentation
- i915 modesetting rework, haswell hdmi, haswell and vlv fixes, write
combined pte writing, ilk rc6 support,
- nouveau: major driver rework into a hw core driver, makes features
like SLI a lot saner to implement,
- psb: add eDP/DP support for Cedarview
- radeon: 2 layer page tables, async VM pte updates, better PLL
selection for > 2 screens, better ACPI interactions
The rest is general grab bag of fixes.
So why part 1? well I have the exynos pull req which came in a bit
late but was waiting for me to do something they shouldn't have and it
looks fairly safe, and David Howells has some more header cleanups
he'd like me to pull, that seem like a good idea, but I'd like to get
this merge out of the way so -next dosen't get blocked."
Tons of conflicts mostly due to silly include line changes, but mostly
mindless. A few other small semantic conflicts too, noted from Dave's
pre-merged branch.
* 'drm-next' of git://people.freedesktop.org/~airlied/linux: (447 commits)
drm/nv98/crypt: fix fuc build with latest envyas
drm/nouveau/devinit: fixup various issues with subdev ctor/init ordering
drm/nv41/vm: fix and enable use of "real" pciegart
drm/nv44/vm: fix and enable use of "real" pciegart
drm/nv04/dmaobj: fixup vm target handling in preparation for nv4x pcie
drm/nouveau: store supported dma mask in vmmgr
drm/nvc0/ibus: initial implementation of subdev
drm/nouveau/therm: add support for fan-control modes
drm/nouveau/hwmon: rename pwm0* to pmw1* to follow hwmon's rules
drm/nouveau/therm: calculate the pwm divisor on nv50+
drm/nouveau/fan: rewrite the fan tachometer driver to get more precision, faster
drm/nouveau/therm: move thermal-related functions to the therm subdev
drm/nouveau/bios: parse the pwm divisor from the perf table
drm/nouveau/therm: use the EXTDEV table to detect i2c monitoring devices
drm/nouveau/therm: rework thermal table parsing
drm/nouveau/gpio: expose the PWM/TOGGLE parameter found in the gpio vbios table
drm/nouveau: fix pm initialization order
drm/nouveau/bios: check that fixed tvdac gpio data is valid before using it
drm/nouveau: log channel debug/error messages from client object rather than drm client
drm/nouveau: have drm debugging macros build on top of core macros
...
Convert #include "..." to #include <path/...> in drivers/gpu/.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Dave Jones <davej@redhat.com>
A side-effect of commit 7d54a90428
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri Aug 10 10:18:10 2012 +0100
drm/i915: Apply post-sync write for pipe control invalidates
was that only a request to emit invalidate flush would result in the
TLB being invalidated (since it requires synchronisation and so incurs a
performance penalty). However, the stated w/a for hardware contexts is
that the TLBs must be invalidated prior to a MI_SET_CONTEXT, yet the w/a
itself did not request the TLBs to be invalidated...
Note this w/a does not prevent the hard system hang I experience when
using hw contexts (with rc6 enabled) on SNB GT1.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Avoid stalling and waiting for the GPU by checking to see if there is
sufficient inactive space in the aperture for us to bind the buffer
prior to writing through the GTT. If there is inadequate space we will
have to stall waiting for the GPU, and incur overheads moving objects
about. Instead, only incur the clflush overhead on the target object by
writing through shmem.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
the following warning was produced,
drivers/gpu/drm/i915/i915_gem_context.c: In function ‘i915_switch_context’:
drivers/gpu/drm/i915/i915_gem_context.c:454:6: warning: unused variable ‘ret’ [-Wunused-variable]
fix up by removing it
Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Basic context support on HSW is no different than previous generations.
The size of the context object changes, but that's about it.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
When bug hunting, I found the interface to do_switch() overly
complicated and I believe festered the earlier bug. This aims to make
the code a little clearer.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
We need to check that "ctx" is a valid pointer before dereferencing it.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Otherwise we end up trying to unpin a freed object and BUG.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
The issue is that we stale data in the CPU caches, when we come to
swap-out the object, the CPU may short-circuit the reads from those
cacheline and so corrupt the context object.
Secondary, leaving the context object as being marked in the CPU write
domain whilst on the GPU active list is a bad idea and will throw
warnings later.
Note: Thanks to calling set_to_gtt_domain with write = false and not
setting any gpu write domain when putting a context object onto the
active list (when we switch away from it) the set_to_gtt_domain call
won't block.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: Added a note to the commit message and a comment in the code
to explain the clever non-blocking trick.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
*sigh* the docs had it spelled wrong, corrected it, and then proceeded
to re-do the original error. The original code preserved this history,
and this patch attempts to keep in sync with the current docs.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Daniel complained about this on initial review, but he graciously moved
the patches forward. As promised, I am delivering the desired cleanup
now.
Hopefully I didn't screw the trivial patch up ;-)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
The idr code already passes us the pointer associated with that id, so
no need to look it up again. Also, we'll kill the idr right away, so
there's no issue with leaving these dangling pointers behind - the
current code does the same.
v2: Also drop the file argument, spotted by Ben Widawsky.
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This is our customary "no such object" errno, not -EINVAL.
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
It doesn't hurt and it at least prevents us from OOPSing left and
right at quite a few places. This also allows us to simplify the code
a bit by folding the only line of context_open into the callsite.
We obviuosly also need to run the cleanup code unconditionally, too.
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
commit 8e96d9c4d9
Author: Ben Widawsky <ben@bwidawsk.net>
Date: Mon Jun 4 14:42:56 2012 -0700
drm/i915: reset the GPU on context fini
broke module unload because it reset the gpu before we've stopped
touching it. Later on in the unload sequence the ringbuffer code
complained that the gpu would idle properly (because intel_gpu_reset
only resets the hw and not our sw state).
v2: Reorder things so that we reset the gpu _before_ we release the
backing storage of the default context.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=51183
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This got dropped as a result of the last round of comments. I didn't
test it on unsupported HW (which this is likely the case).
Note that this prevents hw context from blowing up on any pre-gen6 hw.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=51142
[danvet: Added note and buglink.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Add the interfaces to allow user space to create and destroy contexts.
Contexts are destroyed automatically if the file descriptor for the dri
device is closed.
Following convention as usual here causes checkpatch warnings.
v2: with is_initialized, no longer need to init at create
drop the context switch on create (daniel)
v3: Use interruptible lock (Chris)
return -ENODEV in !GEM case (Chris)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
With the code to do HW context switches in place have the driver load the
default context for the render ring when the driver loads.
The default context will be an ever present context that is available to
switch to at any time for the given ring.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
From http://intellinuxgraphics.org/documentation/SNB/IHD_OS_Vol1_Part3.pdf
[DevSNB] If Flush TLB invalidation Mode is enabled it's the driver's
responsibility to invalidate the TLBs at least once after the previous
context switch after any GTT mappings changed (including new GTT
entries). This can be done by a pipelined PIPE_CONTROL with TLB inv bit
set immediately before MI_SET_CONTEXT.
On GEN7 the invalidation mode is explicitly set, but this appears to be
lacking for GEN6. Since I don't know the history on this, I've decided
to dynamically read the value at ring init time, and use that value
throughout.
v2: better comment (daniel)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
The workaround itself applies to gen7 only (according to the docs) and
as Eric Anholt points out shouldn't be required since we don't use HW
scheduling features, and therefore arbitration. Though since it is a
small, and simple addition, and we don't really understand the issue,
just do it.
FWIW, I eventually want to play with some of the arbitration stuff, and
I'd hate to forget about this.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
This way round we don't introduce and ugly layering violations and use
the interface as I planned to use it.
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Implement the context switch code as well as the interfaces to do the
context switch. This patch also doesn't match 1:1 with the RFC patches.
The main difference is that from Daniel's responses the last context
object is now stored instead of the last context. This aids in allows us
to free the context data structure, and context object independently.
There is room for optimization: this code will pin the context object
until the next context is active. The optimal way to do it is to
actually pin the object, move it to the active list, do the context
switch, and then unpin it. This allows the eviction code to actually
evict the context object if needed.
The context switch code is missing workarounds, they will be implemented
in future patches.
v2: actually do obj->dirty=1 in switch (daniel)
Modified comment around above
Remove flags to context switch (daniel)
Move mi_set_context code to i915_gem_context.c (daniel)
Remove seqno , use lazy request instead (daniel)
v3: use i915_gem_request_next_seqno instead of
outstanding_lazy_request (Daniel)
remove id's from trace events (Daniel)
Put the context BO in the instruction domain (Daniel)
Don't unref the BO is context switch fails (Chris)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Invent an abstraction for a hw context which is passed around through
the core functions. The main bit a hw context holds is the buffer object
which backs the context. The rest of the members are just helper
functions. Specifically the ring member, which could likely go away if
we decide to never implement whatever other hw context support exists.
Of note here is the introduction of the 64k alignment constraint for the
BO. If contexts become heavily used, we should consider tweaking this
down to 4k. Until the contexts are merged and tested a bit though, I
think 64k is a nice start (based on docs).
Since we don't yet switch contexts, there is really not much complexity
here. Creation/destruction works pretty much as one would expect. An idr
is used to generate the context id numbers which are unique per file
descriptor.
v2: add DRM_DEBUG_DRIVERS to distinguish ENOMEM failures (ben)
convert a BUG_ON to WARN_ON, default destruction is still fatal (ben)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Very basic code for context setup/destruction in the driver.
Adds the file i915_gem_context.c This file implements HW context
support. On gen5+ a HW context consists of an opaque GPU object which is
referenced at times of context saves and restores. With RC6 enabled,
the context is also referenced as the GPU enters and exists from RC6
(GPU has it's own internal power context, except on gen5). Though
something like a context does exist for the media ring, the code only
supports contexts for the render ring.
In software, there is a distinction between contexts created by the
user, and the default HW context. The default HW context is used by GPU
clients that do not request setup of their own hardware context. The
default context's state is never restored to help prevent programming
errors. This would happen if a client ran and piggy-backed off another
clients GPU state. The default context only exists to give the GPU some
offset to load as the current to invoke a save of the context we
actually care about. In fact, the code could likely be constructed,
albeit in a more complicated fashion, to never use the default context,
though that limits the driver's ability to swap out, and/or destroy
other contexts.
All other contexts are created as a request by the GPU client. These
contexts store GPU state, and thus allow GPU clients to not re-emit
state (and potentially query certain state) at any time. The kernel
driver makes certain that the appropriate commands are inserted.
There are 4 entry points into the contexts, init, fini, open, close.
The names are self-explanatory except that init can be called during
reset, and also during pm thaw/resume. As we expect our context to be
preserved across these events, we do not reinitialize in this case.
As Adam Jackson pointed out, The cutoff of 1MB where a HW context is
considered too big is arbitrary. The reason for this is even though
context sizes are increasing with every generation, they have yet to
eclipse even 32k. If we somehow read back way more than that, it
probably means BIOS has done something strange, or we're running on a
platform that wasn't designed for this.
v2: rename load/unload to init/fini (daniel)
remove ILK support for get_size() (indirectly daniel)
add HAS_HW_CONTEXTS macro to clarify supported platforms (daniel)
added comments (Ben)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Mika Kuoppala