[Intel-gfx] [PATCH 3/6] drm/i915: Compact memcmp in i915_vma_compare()

[Chris Wilson]

On Wed, Jan 11, 2017 at 09:51:03PM +0000, Chris Wilson wrote:
> In preparation for the next patch to convert to using an anonymous union
> and leaving the excess bytes in the union uninitialised, we first need
> to make sure we do not compare using those uninitialised bytes. We also
> want to preserve the compactness of the code, avoiding a second call to
> memcmp or introducing a switch, so we take advantage of using the type
> as an encoded size (as well as a unique identifier for each type of view).
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.h | 14 +++++++-------
>  drivers/gpu/drm/i915/i915_vma.h     | 15 +++++++++------
>  2 files changed, 16 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
> index 3187a260e6e1..36d85599ffc9 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.h
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
> @@ -145,12 +145,6 @@ typedef uint64_t gen8_ppgtt_pml4e_t;
>  
>  struct sg_table;
>  
> -enum i915_ggtt_view_type {
> -	I915_GGTT_VIEW_NORMAL = 0,
> -	I915_GGTT_VIEW_ROTATED,
> -	I915_GGTT_VIEW_PARTIAL,
> -};
> -
>  struct intel_rotation_info {
>  	struct intel_rotation_plane_info {
>  		/* tiles */
> @@ -184,10 +178,16 @@ static inline u64 intel_partial_get_page_offset(const struct intel_partial_info
>  	return pi->offset_size >> INTEL_PARTIAL_SIZE_BITS;
>  }
>  
> +enum i915_ggtt_view_type {
> +	I915_GGTT_VIEW_NORMAL = 0,
> +	I915_GGTT_VIEW_ROTATED = sizeof(struct intel_rotation_info),
> +	I915_GGTT_VIEW_PARTIAL = sizeof(struct intel_partial_info),

One alternative to packing intel_partial_info into a u64 is to use

I915_GGTT_VIEW_PARTIAL = 12, /* ideal sizeof(struct intel_partial_info) */

How horrible is that?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre