[Intel-gfx] [PATCH v3 2/2] drm/i915: add in-kernel blitter client

[Chris Wilson]

Quoting Matthew Auld (2019-05-21 21:42:35)
> +static void clear_pages_signal_irq_worker(struct irq_work *work)
> +{
> +       struct clear_pages_work *w = container_of(work, typeof(*w), irq_work);
> +
> +       dma_fence_signal(&w->dma);
> +       dma_fence_put(&w->dma);
> +}
> +
> +static void clear_pages_dma_fence_cb(struct dma_fence *fence,
> +                                    struct dma_fence_cb *cb)
> +{
> +       struct clear_pages_work *w = container_of(cb, typeof(*w), cb);

if (fence->error)
	dma_fence_set_error(&w->dma, fence->error);

> +
> +       /*
> +        * Push the signalling of the fence into yet another worker to avoid
> +        * the nightmare locking around the fence spinlock.
> +        */
> +       irq_work_queue(&w->irq_work);
> +}
> +
> +static void clear_pages_worker(struct work_struct *work)
> +{
> +       struct clear_pages_work *w = container_of(work, typeof(*w), work);
> +       struct drm_i915_private *i915 = w->ce->gem_context->i915;
> +       struct drm_i915_gem_object *obj = w->sleeve->obj;
> +       struct i915_vma *vma = w->sleeve->vma;
> +       struct i915_request *rq;
> +       int err = w->dma.error;
> +
> +       if (unlikely(err))
> +               goto out_signal;
> +
> +       if (obj->cache_dirty) {
> +               obj->write_domain = 0;
> +               if (i915_gem_object_has_struct_page(obj))
> +                       drm_clflush_sg(w->sleeve->pages);
> +               obj->cache_dirty = false;
> +       }
> +
> +       mutex_lock(&i915->drm.struct_mutex);
> +       err = i915_vma_pin(vma, 0, 0, PIN_USER);
> +       if (unlikely(err))
> +               goto out_unlock;
> +
> +       rq = i915_request_create(w->ce);
> +       if (IS_ERR(rq)) {
> +               err = PTR_ERR(rq);
> +               goto out_unpin;
> +       }
> +
> +       /* There's no way the fence has signalled */
> +       if (dma_fence_add_callback(&rq->fence, &w->cb,
> +                                  clear_pages_dma_fence_cb))
> +               GEM_BUG_ON(1);
> +
> +       if (w->ce->engine->emit_init_breadcrumb) {
> +               err = w->ce->engine->emit_init_breadcrumb(rq);
> +               if (unlikely(err))
> +                       goto out_request;
> +       }
> +
> +       err = intel_emit_vma_fill_blt(rq, vma, w->value);
> +       if (unlikely(err))
> +               goto out_request;
> +
> +       err = i915_vma_move_to_active(vma, rq, EXEC_OBJECT_WRITE);
> +out_request:
> +       if (unlikely(err)) {
> +               dma_fence_set_error(&w->dma, err);

Propagation should happen via rq signaling.

> +               i915_request_skip(rq, err);
> +               err = 0;
> +       }

So much work to be done to unravel these locks.
-Chris