/**
* i915_switch_context() - perform a GPU context switch.
* @ring: ring for which we'll execute the context switch
* @file_priv: file_priv associated with the context, may be NULL
* @id: context id number
* @seqno: sequence number by which the new context will be switched to
* @flags:
*
* The context life cycle is simple. The context refcount is incremented and
* decremented by 1 and create and destroy. If the context is in use by the GPU,
* it will have a refoucnt > 1. This allows us to destroy the context abstract
* object while letting the normal object tracking destroy the backing BO.
*/
int i915_switch_context(struct intel_ring_buffer *ring,
struct drm_file *file,
int to_id)
{
struct drm_i915_private *dev_priv = ring->dev->dev_private;
struct drm_i915_file_private *file_priv = NULL;
struct i915_hw_context *to;
struct drm_i915_gem_object *from_obj = ring->last_context_obj;
if (dev_priv->hw_contexts_disabled)
return 0;
if (ring != &dev_priv->ring[RCS])
return 0;
if (file)
file_priv = file->driver_priv;
if (to_id == DEFAULT_CONTEXT_ID) {
to = ring->default_context;
} else {
to = i915_gem_context_get(file_priv, to_id);
if (to == NULL)
return -ENOENT;
}
if (from_obj == to->obj)
return 0;
return do_switch(from_obj, to, i915_gem_next_request_seqno(to->ring));
}
static int do_switch(struct i915_hw_context *to)
{
struct intel_ring_buffer *ring = to->ring;
struct drm_i915_gem_object *from_obj = ring->last_context_obj;
u32 hw_flags = 0;
int ret;
KASSERT(!(from_obj != NULL && from_obj->pin_count == 0),
("i915_gem_context: invalid \"from\" context"));
if (from_obj == to->obj)
return 0;
ret = i915_gem_object_pin(to->obj, CONTEXT_ALIGN, false);
if (ret)
return ret;
/* Clear this page out of any CPU caches for coherent swap-in/out. Note
* that thanks to write = false in this call and us not setting any gpu
* write domains when putting a context object onto the active list
* (when switching away from it), this won't block.
* XXX: We need a real interface to do this instead of trickery. */
ret = i915_gem_object_set_to_gtt_domain(to->obj, false);
if (ret) {
i915_gem_object_unpin(to->obj);
return ret;
}
if (!to->obj->has_global_gtt_mapping)
i915_gem_gtt_bind_object(to->obj, to->obj->cache_level);
if (!to->is_initialized || is_default_context(to))
hw_flags |= MI_RESTORE_INHIBIT;
else if (from_obj == to->obj) /* not yet expected */
hw_flags |= MI_FORCE_RESTORE;
ret = mi_set_context(ring, to, hw_flags);
if (ret) {
i915_gem_object_unpin(to->obj);
return ret;
}
/* The backing object for the context is done after switching to the
* *next* context. Therefore we cannot retire the previous context until
* the next context has already started running. In fact, the below code
* is a bit suboptimal because the retiring can occur simply after the
* MI_SET_CONTEXT instead of when the next seqno has completed.
*/
if (from_obj != NULL) {
from_obj->base.read_domains = I915_GEM_DOMAIN_INSTRUCTION;
i915_gem_object_move_to_active(from_obj, ring,
i915_gem_next_request_seqno(ring));
/* As long as MI_SET_CONTEXT is serializing, ie. it flushes the
* whole damn pipeline, we don't need to explicitly mark the
* object dirty. The only exception is that the context must be
* correct in case the object gets swapped out. Ideally we'd be
* able to defer doing this until we know the object would be
* swapped, but there is no way to do that yet.
*/
from_obj->dirty = 1;
KASSERT(from_obj->ring == ring, ("i915_gem_context: from_ring != ring"));
i915_gem_object_unpin(from_obj);
drm_gem_object_unreference(&from_obj->base);
}
drm_gem_object_reference(&to->obj->base);
ring->last_context_obj = to->obj;
to->is_initialized = true;
return 0;
}
