[Intel-gfx] [PATCH 24/51] drm/i915: Update deferred context creation to do explicit request management

[John.C.Harrison at Intel.com]

From: John Harrison <John.C.Harrison at Intel.com>

In execlist mode, context initialisation is deferred until first use of the
given context. This is because execlist mode has many more contexts than legacy
mode and many are never actually used. Previously, the initialisation commands
were written to the ring and tagged with some random request structure via the
OLR. This seemed to be causing a null pointer deference bug under certain
circumstances (BZ:40112).

This patch adds explicit request creation and submission to the deferred
initialisation code path. Thus removing any reliance on or randomness caused by
the OLR.

For: VIZ-5115
Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
---
 drivers/gpu/drm/i915/intel_lrc.c |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index de01cae..2882d3f 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1822,6 +1822,7 @@ static void lrc_setup_hardware_status_page(struct intel_engine_cs *ring,
 int intel_lr_context_deferred_create(struct intel_context *ctx,
 				     struct intel_engine_cs *ring)
 {
+	struct drm_i915_private *dev_priv = ring->dev->dev_private;
 	const bool is_global_default_ctx = (ctx == ring->default_context);
 	struct drm_device *dev = ring->dev;
 	struct drm_i915_gem_object *ctx_obj;
@@ -1902,13 +1903,27 @@ int intel_lr_context_deferred_create(struct intel_context *ctx,
 		lrc_setup_hardware_status_page(ring, ctx_obj);
 	else if (ring->id == RCS && !ctx->rcs_initialized) {
 		if (ring->init_context) {
-			ret = ring->init_context(ring, ctx);
+			struct drm_i915_gem_request *req;
+
+			ret = dev_priv->gt.alloc_request(ring, ctx, &req);
+			if (ret)
+				return ret;
+
+			ret = ring->init_context(req->ring, ctx);
 			if (ret) {
 				DRM_ERROR("ring init context: %d\n", ret);
+				i915_gem_request_unreference(req);
 				ctx->engine[ring->id].ringbuf = NULL;
 				ctx->engine[ring->id].state = NULL;
 				goto error;
 			}
+
+			ret = i915_add_request_no_flush(req->ring);
+			if (ret) {
+				DRM_ERROR("ring init context: %d\n", ret);
+				i915_gem_request_unreference(req);
+				goto error;
+			}
 		}
 
 		ctx->rcs_initialized = true;
-- 
1.7.9.5