drm/i915: Add *_ring_begin() to request allocation

Now that the *_ring_begin() functions no longer call the request allocation
code, it is finally safe for the request allocation code to call *_ring_begin().
This is important to guarantee that the space reserved for the subsequent
i915_add_request() call does actually get reserved.

v2: Renamed functions according to review feedback (Tomas Elf).

For: VIZ-5115
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 15 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index ad9db8a79d08..75c3b9dfec9e 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -834,6 +834,21 @@ static int intel_logical_ring_begin(struct drm_i915_gem_request *req,
 	return 0;
 }
 
+int intel_logical_ring_reserve_space(struct drm_i915_gem_request *request)
+{
+	/*
+	 * The first call merely notes the reserve request and is common for
+	 * all back ends. The subsequent localised _begin() call actually
+	 * ensures that the reservation is available. Without the begin, if
+	 * the request creator immediately submitted the request without
+	 * adding any commands to it then there might not actually be
+	 * sufficient room for the submission commands.
+	 */
+	intel_ring_reserved_space_reserve(request->ringbuf, MIN_SPACE_FOR_ADD_REQUEST);
+
+	return intel_logical_ring_begin(request, 0);
+}
+
 /**
  * execlists_submission() - submit a batchbuffer for execution, Execlists style
  * @dev: DRM device.