[Intel-gfx] [PATCH 25/59] 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:88865).

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.

Note that it should be possible to move the deferred context creation until even
later - when the context is actually switched to rather than when it is merely
validated. This would allow the initialisation to be done within the request of
the work that is wanting to use the context. Hence, the extra request that is
created, used and retired just for the context init could be removed completely.
However, this is left for a follow up patch.

For: VIZ-5115
Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
---
 drivers/gpu/drm/i915/intel_lrc.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index b430e51..c77a74b 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1949,13 +1949,22 @@ 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 = i915_gem_request_alloc(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_cancel(req);
 				ctx->engine[ring->id].ringbuf = NULL;
 				ctx->engine[ring->id].state = NULL;
 				goto error;
 			}
+
+			i915_add_request_no_flush(req->ring);
 		}
 
 		ctx->rcs_initialized = true;
-- 
1.7.9.5