[Intel-gfx] [PATCH v10 2/6] drm/i915: Convert requests to use struct fence

[Maarten Lankhorst]

Op 16-06-16 om 14:54 schreef John.C.Harrison at Intel.com:
> From: John Harrison <John.C.Harrison at Intel.com>
>
> There is a construct in the linux kernel called 'struct fence' that is
> intended to keep track of work that is executed on hardware. I.e. it
> solves the basic problem that the drivers 'struct
> drm_i915_gem_request' is trying to address. The request structure does
> quite a lot more than simply track the execution progress so is very
> definitely still required. However, the basic completion status side
> could be updated to use the ready made fence implementation and gain
> all the advantages that provides.
>
> This patch makes the first step of integrating a struct fence into the
> request. It replaces the explicit reference count with that of the
> fence. It also replaces the 'is completed' test with the fence's
> equivalent. Currently, that simply chains on to the original request
> implementation. A future patch will improve this.
>
> v3: Updated after review comments by Tvrtko Ursulin. Added fence
> context/seqno pair to the debugfs request info. Renamed fence 'driver
> name' to just 'i915'. Removed BUG_ONs.
>
> v5: Changed seqno format in debugfs to %x rather than %u as that is
> apparently the preferred appearance. Line wrapped some long lines to
> keep the style checker happy.
>
> v6: Updated to newer nigthly and resolved conflicts. The biggest issue
> was with the re-worked busy spin precursor to waiting on a request. In
> particular, the addition of a 'request_started' helper function. This
> has no corresponding concept within the fence framework. However, it
> is only ever used in one place and the whole point of that place is to
> always directly read the seqno for absolutely lowest latency possible.
> So the simple solution is to just make the seqno test explicit at that
> point now rather than later in the series (it was previously being
> done anyway when fences become interrupt driven).
>
> v7: Rebased to newer nightly - lots of ring -> engine renaming and
> interface change to get_seqno().
>
> v8: Rebased to newer nightly - no longer needs to worry about mutex
> locking in the request free code path. Moved to after fence timeline
> patch so no longer needs to add a horrid hack timeline.
>
> Removed commented out code block. Added support for possible RCU usage
> of fence object (Review comments by Maarten Lankhorst).
>
> v10: Removed duplicate rcu_head field from request - there is already
> one in the fence structure for this exact purpose. Improved/added some
> comments. [Review comments from Maarten Lankhorst & Tvrtko Ursulin]
>
> Updated for yet more nightly changes (u64 for fence context).
Reviewed-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>