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

Tvrtko Ursulin
2016-01-11T17:44:57Z

On 11/01/16 16:16, Dave Gordon wrote:
> 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:

Oh yes, it crossed my mind and then I forgot about it, so thanks!

> #define I915_GTT_BAD_ADDRESS (~(u64)0)

It would match current behaviour of i915_gem_obj_offset(_view) of
returning -1 when VMA is not found so I think it is good enough to go
with this approach.

Regards,

Tvrtko