Re: [PATCH 50/53] drm/i915: Update intel_logical_ring_begin() to take a request structure

[Tomas Elf <tomas.elf@intel.com>]

On 19/02/2015 17:18, John.C.Harrison@Intel.com wrote:
> From: John Harrison <John.C.Harrison@Intel.com>
>
> Now that everything above has been converted to use requests,
> intel_logical_ring_begin() can be updated to take a request instead of a
> ringbuf/context pair. This also means that it no longer needs to lazily allocate
> a request if no-one happens to have done it earlier.
>
> Note that this change makes the execlist signature the same as the legacy
> version. Thus the two functions could be merged into a ring->begin() wrapper if
> required.
>
> For: VIZ-5115
> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
> ---
>   drivers/gpu/drm/i915/intel_lrc.c |   33 +++++++++++++++------------------
>   1 file changed, 15 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index b40501d..2911cf6 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -766,7 +766,7 @@ static int logical_ring_prepare(struct intel_ringbuffer *ringbuf,
>   /**
>    * intel_logical_ring_begin() - prepare the logical ringbuffer to accept some commands
>    *
> - * @ringbuf: Logical ringbuffer.
> + * @request: The request to start some new work for
>    * @num_dwords: number of DWORDs that we plan to write to the ringbuffer.
>    *
>    * The ringbuffer might not be ready to accept the commands right away (maybe it needs to
> @@ -776,30 +776,27 @@ static int logical_ring_prepare(struct intel_ringbuffer *ringbuf,
>    *
>    * Return: non-zero if the ringbuffer is not ready to be written to.
>    */
> -static int intel_logical_ring_begin(struct intel_ringbuffer *ringbuf,
> -				    struct intel_context *ctx, int num_dwords)
> +static int intel_logical_ring_begin(struct drm_i915_gem_request *req,
> +				    int num_dwords)
>   {
> -	struct drm_i915_gem_request *req;
> -	struct intel_engine_cs *ring = ringbuf->ring;
> +	struct intel_engine_cs *ring = req->ring;
>   	struct drm_device *dev = ring->dev;
>   	struct drm_i915_private *dev_priv = dev->dev_private;
>   	int ret;
>
> +	WARN_ON(req == NULL);

This WARN_ON will only fire after there's been a null pointer exception 
in the req->ring dereference above. Please rearrange these so that it 
warns before the null pointer exception.

Thanks,
Tomas

> +
>   	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
>   				   dev_priv->mm.interruptible);
>   	if (ret)
>   		return ret;
>
> -	ret = logical_ring_prepare(ringbuf, ctx, num_dwords * sizeof(uint32_t));
> -	if (ret)
> -		return ret;
> -
> -	/* Preallocate the olr before touching the ring */
> -	ret = intel_logical_ring_alloc_request(ring, ctx, &req);
> +	ret = logical_ring_prepare(req->ringbuf, req->ctx,
> +				   num_dwords * sizeof(uint32_t));
>   	if (ret)
>   		return ret;
>
> -	ringbuf->space -= num_dwords * sizeof(uint32_t);
> +	req->ringbuf->space -= num_dwords * sizeof(uint32_t);
>   	return 0;
>   }
>
> @@ -885,7 +882,7 @@ int intel_execlists_submission(struct i915_execbuffer_params *params,
>
>   	if (ring == &dev_priv->ring[RCS] &&
>   	    instp_mode != dev_priv->relative_constants_mode) {
> -		ret = intel_logical_ring_begin(ringbuf, params->ctx, 4);
> +		ret = intel_logical_ring_begin(params->request, 4);
>   		if (ret)
>   			return ret;
>
> @@ -1091,7 +1088,7 @@ static int intel_logical_ring_workarounds_emit(struct drm_i915_gem_request *req)
>   	if (ret)
>   		return ret;
>
> -	ret = intel_logical_ring_begin(ringbuf, req->ctx, w->count * 2 + 2);
> +	ret = intel_logical_ring_begin(req, w->count * 2 + 2);
>   	if (ret)
>   		return ret;
>
> @@ -1173,7 +1170,7 @@ static int gen8_emit_bb_start(struct drm_i915_gem_request *req,
>   	bool ppgtt = !(dispatch_flags & I915_DISPATCH_SECURE);
>   	int ret;
>
> -	ret = intel_logical_ring_begin(ringbuf, req->ctx, 4);
> +	ret = intel_logical_ring_begin(req, 4);
>   	if (ret)
>   		return ret;
>
> @@ -1231,7 +1228,7 @@ static int gen8_emit_flush(struct drm_i915_gem_request *request,
>   	uint32_t cmd;
>   	int ret;
>
> -	ret = intel_logical_ring_begin(ringbuf, request->ctx, 4);
> +	ret = intel_logical_ring_begin(request, 4);
>   	if (ret)
>   		return ret;
>
> @@ -1289,7 +1286,7 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
>   		flags |= PIPE_CONTROL_GLOBAL_GTT_IVB;
>   	}
>
> -	ret = intel_logical_ring_begin(ringbuf, request->ctx, 6);
> +	ret = intel_logical_ring_begin(request, 6);
>   	if (ret)
>   		return ret;
>
> @@ -1321,7 +1318,7 @@ static int gen8_emit_request(struct drm_i915_gem_request *request)
>   	u32 cmd;
>   	int ret;
>
> -	ret = intel_logical_ring_begin(ringbuf, request->ctx, 6);
> +	ret = intel_logical_ring_begin(request, 6);
>   	if (ret)
>   		return ret;
>
>

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