Re: [PATCH v4] drm/i915: Small compaction of the engine init code

Chris Wilson
2016-06-23T14:03:28Z

On Thu, Jun 23, 2016 at 02:52:41PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> Effectively removes one layer of indirection between the mask of
> possible engines and the engine constructors. Instead of spelling
> out in code the mapping of HAS_<engine> to constructors, makes
> more use of the recently added data driven approach by putting
> engine constructor vfuncs into the table as well.
>
> Effect is fewer lines of source and smaller binary.
>
> At the same time simplify the error handling since engine
> destructors can run on unitialized engines anyway.
>
> Similar approach could be done for legacy submission is wanted.
>
> v2: Removed ugly BUILD_BUG_ONs in favour of newly introduced
> ENGINE_MASK and HAS_ENGINE macros.
> Also removed the forward declarations by shuffling functions
> around.
>
> v3: Warn when logical_rings table does not contain enough data
> and disable the engines which could not be initialized.
> (Chris Wilson)
>
> v4: Chris Wilson suggested a nicer engine init loop.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

> + WARN_ON(INTEL_INFO(dev_priv)->ring_mask &
> + GENMASK(sizeof(mask) * BITS_PER_BYTE - 1, I915_NUM_ENGINES));

It's computed as a long, so BITS_PER_LONG would suffice

p/x GENMASK(sizeof(mask) * BITS_PER_BYTE - 1, I915_NUM_ENGINES))
= ((~0UL) << I915_NUM_ENGINES)
= 0xffffffc0

p/x -(1 << I915_NUM_ENGINES)
= 0xffffffc0

--
Chris Wilson, Intel Open Source Technology Centre