[Intel-gfx] [PATCH 46/55] drm/i915: Update intel_ring_begin() to take a request structure

[John Harrison]

On 23/06/2015 11:24, Chris Wilson wrote:
> On Fri, May 29, 2015 at 05:44:07PM +0100, John.C.Harrison at Intel.com wrote:
>> -int intel_ring_begin(struct intel_engine_cs *ring,
>> +int intel_ring_begin(struct drm_i915_gem_request *req,
>>   		     int num_dwords)
>>   {
>> -	struct drm_i915_gem_request *req;
>> -	struct drm_i915_private *dev_priv = ring->dev->dev_private;
>> +	struct intel_engine_cs *ring;
>> +	struct drm_i915_private *dev_priv;
>>   	int ret;
>>   
>> +	WARN_ON(req == NULL);
>> +	ring = req->ring;
> What was the point?
> -Chris
>

The point is to remove the OLR. The significant change within 
intel_ring_begin is the next few lines:

-	/* Preallocate the olr before touching the ring */
-	ret = i915_gem_request_alloc(ring, ring->default_context, &req);


That is the part that causes problems by randomly creating a brand new 
request that no-one knows about and squirreling it away in the OLR to 
scoop up random bits of work. This is the whole point of the entire 
patch series - to ensure that all ring work is assigned to a known 
request by whoever instigated that work.

John.