Quoting changbin.du@xxxxxxxxx (2017-09-01 08:08:26)
> diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.c b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
> index 5fe2cd8..429ce5f 100644
> --- a/drivers/gpu/drm/i915/i915_gem_fence_reg.c
> +++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
> @@ -360,6 +360,50 @@ i915_vma_get_fence(struct i915_vma *vma)
> }
>
> /**
> + * i915_reserve_fence - Reserve a fence for vGPU
> + * @dev_priv: i915 device private
> + *
> + * This function walks the fence regs looking for a free one and remove
> + * it from the fence_list. It is used to reserve fence for vGPU to use.
> + */
> +struct drm_i915_fence_reg *
> +i915_reserve_fence(struct drm_i915_private *dev_priv)
> +{
> + struct drm_i915_fence_reg *fence;
> + int ret;
lockdep_assert_held(&dev_priv->drm.struct_mutex);
A reminder for when we move fences to a seperate mutex.
> +
> + /* Host at least need one fence available for display engine. */
> + if (unlikely(dev_priv->mm.fence_list.prev ==
> + dev_priv->mm.fence_list.next))
> + return ERR_PTR(-ENOSPC);
I would prefer one free fence.
int count;
/* Keep at least one fence available for the display engine */
count = 0;
list_for_each_entry(fence, &dev_priv->mm.fence_list, link)
count += !fence->pin_count;
if (count <= 1)
return ERR_PTR(-ENOSPC);
> +
> + fence = fence_find(dev_priv);
> + if (IS_ERR(fence))
> + return fence;
> +
> + if (fence->vma) {
> + /* Force-remove fence from VMA */
> + ret = fence_update(fence, NULL);
> + if (ret)
> + return ERR_PTR(ret);
> + }
> +
> + list_del(&fence->link);
> + return fence;
> +}
> +
> +/**
> + * i915_unreserve_fence - Reclaim a reserved fence
> + * @fence: the fence reg
> + *
> + * This function add a reserved fence register from vGPU to the fence_list.
> + */
> +void i915_unreserve_fence(struct drm_i915_fence_reg *fence)
> +{
lockdep_assert_held(&dev_priv->drm.struct_mutex);
If you agree to "one free fence",
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Otherwise, we need to look carefully at what happens when the search
fails. And that may suggest we need to keep one free per crtc, or that
we can survive without (but that usually means giving up on fbc and
whatnot, thinking of fbc is why I want to keep one spare).
(Time to write some unittests for find-a-fence.)
-Chris
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