Re: [PATCH 11/13] drm/i915: Cache ringbuffer GTT address

Dave Gordon
2016-01-11T16:16:30Z

On 08/01/16 11:29, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> Purpose is to avoid calling i915_gem_obj_ggtt_offset from the
> interrupt context without the big lock held.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
> drivers/gpu/drm/i915/intel_lrc.c | 3 +--
> drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++
> drivers/gpu/drm/i915/intel_ringbuffer.h | 1 +
> 3 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 5b3795815d8e..70c511ef6b12 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -345,7 +345,6 @@ static int execlists_update_context(struct drm_i915_gem_request *rq)
> struct intel_engine_cs *ring = rq->ring;
> struct i915_hw_ppgtt *ppgtt = rq->ctx->ppgtt;
> struct drm_i915_gem_object *ctx_obj = rq->ctx->engine[ring->id].state;
> - struct drm_i915_gem_object *rb_obj = rq->ringbuf->obj;
> struct page *page;
> uint32_t *reg_state;
>
> @@ -355,7 +354,7 @@ static int execlists_update_context(struct drm_i915_gem_request *rq)
> reg_state = kmap_atomic(page);
>
> reg_state[CTX_RING_TAIL+1] = rq->tail;
> - reg_state[CTX_RING_BUFFER_START+1] = i915_gem_obj_ggtt_offset(rb_obj);
> + reg_state[CTX_RING_BUFFER_START+1] = rq->ringbuf->gtt_start;
>
> if (ppgtt && !USES_FULL_48BIT_PPGTT(ppgtt->base.dev)) {
> /* True 32b PPGTT with dynamic page allocation: update PDP
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 339701d7a9a5..9094ce254125 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1988,6 +1988,7 @@ void intel_unpin_ringbuffer_obj(struct intel_ringbuffer *ringbuf)
> else
> iounmap(ringbuf->virtual_start);
> ringbuf->virtual_start = NULL;
> + ringbuf->gtt_start = 0;

Zero isn't an invalid GTT address (although it does cause confusion).
Maybe we should define a suitable value to indicate not-an-address?
Anything with low bits set, or above 4Gb, is not valid, so perhaps:

#define I915_GTT_BAD_ADDRESS (~(u64)0)

.Dave.

> i915_gem_object_ggtt_unpin(ringbuf->obj);
> }
>
> @@ -2054,6 +2055,8 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
> }
> }
>
> + ringbuf->gtt_start = i915_gem_obj_ggtt_offset(obj);
> +
> return 0;
> }
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 0b91a4b77359..25d3716228ae 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -98,6 +98,7 @@ struct intel_ring_hangcheck {
> struct intel_ringbuffer {
> struct drm_i915_gem_object *obj;
> void __iomem *virtual_start;
> + u64 gtt_start;
>
> struct intel_engine_cs *ring;
> struct list_head link;