Re: [PATCH v3 1/3] drm/i915: simplify allocation of driver-internal requests

[Nick Hoath <nicholas.hoath@intel.com>]

On 07/01/2016 10:20, Dave Gordon wrote:
> There are a number of places where the driver needs a request, but isn't
> working on behalf of any specific user or in a specific context. At
> present, we associate them with the per-engine default context. A future
> patch will abolish those per-engine context pointers; but we can already
> eliminate a lot of the references to them, just by making the allocator
> allow NULL as a shorthand for "an appropriate context for this ring",
> which will mean that the callers don't need to know anything about how
> the "appropriate context" is found (e.g. per-ring vs per-device, etc).
>
> So this patch renames the existing i915_gem_request_alloc(), and makes
> it local (static inline), and replaces it with a wrapper that provides
> a default if the context is NULL, and also has a nicer calling
> convention (doesn't require a pointer to an output parameter). Then we
> change all callers to use the new convention:
> OLD:
> 	err = i915_gem_request_alloc(ring, user_ctx, &req);
> 	if (err) ...
> NEW:
> 	req = i915_gem_request_alloc(ring, user_ctx);
> 	if (IS_ERR(req)) ...
> OLD:
> 	err = i915_gem_request_alloc(ring, ring->default_context, &req);
> 	if (err) ...
> NEW:
> 	req = i915_gem_request_alloc(ring, NULL);
> 	if (IS_ERR(req)) ...
>
> Signed-off-by: Dave Gordon <david.s.gordon@intel.com>

Reviewed-by: Nick Hoath <nicholas.hoath@intel.com>

> ---
>   drivers/gpu/drm/i915/i915_drv.h            |  6 ++--
>   drivers/gpu/drm/i915/i915_gem.c            | 55 +++++++++++++++++++++++-------
>   drivers/gpu/drm/i915/i915_gem_execbuffer.c | 14 +++++---
>   drivers/gpu/drm/i915/intel_display.c       |  6 ++--
>   drivers/gpu/drm/i915/intel_lrc.c           |  9 +++--
>   drivers/gpu/drm/i915/intel_overlay.c       | 24 ++++++-------
>   6 files changed, 74 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index c6dd4db..c2b000a 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2260,9 +2260,9 @@ struct drm_i915_gem_request {
>
>   };
>
> -int i915_gem_request_alloc(struct intel_engine_cs *ring,
> -			   struct intel_context *ctx,
> -			   struct drm_i915_gem_request **req_out);
> +struct drm_i915_gem_request * __must_check
> +i915_gem_request_alloc(struct intel_engine_cs *engine,
> +		       struct intel_context *ctx);
>   void i915_gem_request_cancel(struct drm_i915_gem_request *req);
>   void i915_gem_request_free(struct kref *req_ref);
>   int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 6c60e04..c908ed1 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2688,9 +2688,10 @@ void i915_gem_request_free(struct kref *req_ref)
>   	kmem_cache_free(req->i915->requests, req);
>   }
>
> -int i915_gem_request_alloc(struct intel_engine_cs *ring,
> -			   struct intel_context *ctx,
> -			   struct drm_i915_gem_request **req_out)
> +static inline int
> +__i915_gem_request_alloc(struct intel_engine_cs *ring,
> +			 struct intel_context *ctx,
> +			 struct drm_i915_gem_request **req_out)
>   {
>   	struct drm_i915_private *dev_priv = to_i915(ring->dev);
>   	struct drm_i915_gem_request *req;
> @@ -2753,6 +2754,31 @@ err:
>   	return ret;
>   }
>
> +/**
> + * i915_gem_request_alloc - allocate a request structure
> + *
> + * @engine: engine that we wish to issue the request on.
> + * @ctx: context that the request will be associated with.
> + *       This can be NULL if the request is not directly related to
> + *       any specific user context, in which case this function will
> + *       choose an appropriate context to use.
> + *
> + * Returns a pointer to the allocated request if successful,
> + * or an error code if not.
> + */
> +struct drm_i915_gem_request *
> +i915_gem_request_alloc(struct intel_engine_cs *engine,
> +		       struct intel_context *ctx)
> +{
> +	struct drm_i915_gem_request *req;
> +	int err;
> +
> +	if (ctx == NULL)
> +		ctx = engine->default_context;
> +	err = __i915_gem_request_alloc(engine, ctx, &req);
> +	return err ? ERR_PTR(err) : req;
> +}
> +
>   void i915_gem_request_cancel(struct drm_i915_gem_request *req)
>   {
>   	intel_ring_reserved_space_cancel(req->ringbuf);
> @@ -3170,9 +3196,13 @@ __i915_gem_object_sync(struct drm_i915_gem_object *obj,
>   			return 0;
>
>   		if (*to_req == NULL) {
> -			ret = i915_gem_request_alloc(to, to->default_context, to_req);
> -			if (ret)
> -				return ret;
> +			struct drm_i915_gem_request *req;
> +
> +			req = i915_gem_request_alloc(to, NULL);
> +			if (IS_ERR(req))
> +				return PTR_ERR(req);
> +
> +			*to_req = req;
>   		}
>
>   		trace_i915_gem_ring_sync_to(*to_req, from, from_req);
> @@ -3372,9 +3402,9 @@ int i915_gpu_idle(struct drm_device *dev)
>   		if (!i915.enable_execlists) {
>   			struct drm_i915_gem_request *req;
>
> -			ret = i915_gem_request_alloc(ring, ring->default_context, &req);
> -			if (ret)
> -				return ret;
> +			req = i915_gem_request_alloc(ring, NULL);
> +			if (IS_ERR(req))
> +				return PTR_ERR(req);
>
>   			ret = i915_switch_context(req);
>   			if (ret) {
> @@ -4869,10 +4899,9 @@ i915_gem_init_hw(struct drm_device *dev)
>   	for_each_ring(ring, dev_priv, i) {
>   		struct drm_i915_gem_request *req;
>
> -		WARN_ON(!ring->default_context);
> -
> -		ret = i915_gem_request_alloc(ring, ring->default_context, &req);
> -		if (ret) {
> +		req = i915_gem_request_alloc(ring, NULL);
> +		if (IS_ERR(req)) {
> +			ret = PTR_ERR(req);
>   			i915_gem_cleanup_ringbuffer(dev);
>   			goto out;
>   		}
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index dccb517..dc6caeb 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -1381,6 +1381,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
>   		       struct drm_i915_gem_exec_object2 *exec)
>   {
>   	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct drm_i915_gem_request *req = NULL;
>   	struct eb_vmas *eb;
>   	struct drm_i915_gem_object *batch_obj;
>   	struct drm_i915_gem_exec_object2 shadow_exec_entry;
> @@ -1602,11 +1603,13 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
>   		params->batch_obj_vm_offset = i915_gem_obj_offset(batch_obj, vm);
>
>   	/* Allocate a request for this batch buffer nice and early. */
> -	ret = i915_gem_request_alloc(ring, ctx, &params->request);
> -	if (ret)
> +	req = i915_gem_request_alloc(ring, ctx);
> +	if (IS_ERR(req)) {
> +		ret = PTR_ERR(req);
>   		goto err_batch_unpin;
> +	}
>
> -	ret = i915_gem_request_add_to_client(params->request, file);
> +	ret = i915_gem_request_add_to_client(req, file);
>   	if (ret)
>   		goto err_batch_unpin;
>
> @@ -1622,6 +1625,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
>   	params->dispatch_flags          = dispatch_flags;
>   	params->batch_obj               = batch_obj;
>   	params->ctx                     = ctx;
> +	params->request                 = req;
>
>   	ret = dev_priv->gt.execbuf_submit(params, args, &eb->vmas);
>
> @@ -1645,8 +1649,8 @@ err:
>   	 * must be freed again. If it was submitted then it is being tracked
>   	 * on the active request list and no clean up is required here.
>   	 */
> -	if (ret && params->request)
> -		i915_gem_request_cancel(params->request);
> +	if (ret && req)
> +		i915_gem_request_cancel(req);
>
>   	mutex_unlock(&dev->struct_mutex);
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index ed9ab60..1f8f781 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -11700,9 +11700,11 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>   					obj->last_write_req);
>   	} else {
>   		if (!request) {
> -			ret = i915_gem_request_alloc(ring, ring->default_context, &request);
> -			if (ret)
> +			request = i915_gem_request_alloc(ring, NULL);
> +			if (IS_ERR(request)) {
> +				ret = PTR_ERR(request);
>   				goto cleanup_unpin;
> +			}
>   		}
>
>   		ret = dev_priv->display.queue_flip(dev, crtc, fb, obj, request,
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 8096c6a..8b6542d 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -2510,11 +2510,10 @@ int intel_lr_context_deferred_alloc(struct intel_context *ctx,
>   	if (ctx != ring->default_context && ring->init_context) {
>   		struct drm_i915_gem_request *req;
>
> -		ret = i915_gem_request_alloc(ring,
> -			ctx, &req);
> -		if (ret) {
> -			DRM_ERROR("ring create req: %d\n",
> -				ret);
> +		req = i915_gem_request_alloc(ring, ctx);
> +		if (IS_ERR(req)) {
> +			ret = PTR_ERR(req);
> +			DRM_ERROR("ring create req: %d\n", ret);
>   			goto error_ringbuf;
>   		}
>
> diff --git a/drivers/gpu/drm/i915/intel_overlay.c b/drivers/gpu/drm/i915/intel_overlay.c
> index 76f1980..9168413 100644
> --- a/drivers/gpu/drm/i915/intel_overlay.c
> +++ b/drivers/gpu/drm/i915/intel_overlay.c
> @@ -240,9 +240,9 @@ static int intel_overlay_on(struct intel_overlay *overlay)
>   	WARN_ON(overlay->active);
>   	WARN_ON(IS_I830(dev) && !(dev_priv->quirks & QUIRK_PIPEA_FORCE));
>
> -	ret = i915_gem_request_alloc(ring, ring->default_context, &req);
> -	if (ret)
> -		return ret;
> +	req = i915_gem_request_alloc(ring, NULL);
> +	if (IS_ERR(req))
> +		return PTR_ERR(req);
>
>   	ret = intel_ring_begin(req, 4);
>   	if (ret) {
> @@ -283,9 +283,9 @@ static int intel_overlay_continue(struct intel_overlay *overlay,
>   	if (tmp & (1 << 17))
>   		DRM_DEBUG("overlay underrun, DOVSTA: %x\n", tmp);
>
> -	ret = i915_gem_request_alloc(ring, ring->default_context, &req);
> -	if (ret)
> -		return ret;
> +	req = i915_gem_request_alloc(ring, NULL);
> +	if (IS_ERR(req))
> +		return PTR_ERR(req);
>
>   	ret = intel_ring_begin(req, 2);
>   	if (ret) {
> @@ -349,9 +349,9 @@ static int intel_overlay_off(struct intel_overlay *overlay)
>   	 * of the hw. Do it in both cases */
>   	flip_addr |= OFC_UPDATE;
>
> -	ret = i915_gem_request_alloc(ring, ring->default_context, &req);
> -	if (ret)
> -		return ret;
> +	req = i915_gem_request_alloc(ring, NULL);
> +	if (IS_ERR(req))
> +		return PTR_ERR(req);
>
>   	ret = intel_ring_begin(req, 6);
>   	if (ret) {
> @@ -423,9 +423,9 @@ static int intel_overlay_release_old_vid(struct intel_overlay *overlay)
>   		/* synchronous slowpath */
>   		struct drm_i915_gem_request *req;
>
> -		ret = i915_gem_request_alloc(ring, ring->default_context, &req);
> -		if (ret)
> -			return ret;
> +		req = i915_gem_request_alloc(ring, NULL);
> +		if (IS_ERR(req))
> +			return PTR_ERR(req);
>
>   		ret = intel_ring_begin(req, 2);
>   		if (ret) {
>

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