[Intel-gfx] [PATCH v3] drm/i915: Add interface to reserve fence registers for vGPU

[Chris Wilson]

Quoting changbin.du at intel.com (2017-09-04 09:01:01)
> From: Changbin Du <changbin.du at intel.com>
> 
> In the past, vGPU alloc fence registers by walking through mm.fence_list
> to find fence which pin_count = 0 and vma is empty. vGPU may not find
> enough fence registers this way. Because a fence can be bind to vma even
> though it is not in using. We have found such failure many times these
> days.
> 
> An option to resolve this issue is that we can force-remove fence from
> vma in this case.
> 
> This patch added two new api to the fence management code:
>  - i915_reserve_fence() will try to find a free fence from fence_list
>    and force-remove vma if need.
>  - i915_unreserve_fence() reclaim a reserved fence after vGPU has
>    finished.
> 
> With this change, the fence management is more clear to work with vGPU.
> GVTg do not need remove fence from fence_list in private.
> 
> v3: (Chris)
>   - Add struct_mutex lock assertion.
>   - Only count for unpinned fence.
> 
> v2: (Chris)
>   - Rename the new api for symmetry.
>   - Add safeguard to ensure at least 1 fence remained for host display.
> 
> Signed-off-by: Changbin Du <changbin.du at intel.com>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

Anyone want to give an ack/review for the GVT side, and then I'll push.
-Chris