drm/i915/perf: Fix OA context id overlap with idle context id

Engine context pinned in perf OA was set to same context id as
the idle context. Set the context id to an unused value.

Clear the sw context id field in lrc descriptor before ORing with
ce->tag (Chris)

Closes: https://gitlab.freedesktop.org/drm/intel/issues/756Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200124013701.40609-1-umesh.nerlige.ramappa@intel.com

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -1211,12 +1211,12 @@ __execlists_schedule_in(struct i915_request *rq)
 	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
 		execlists_check_context(ce, engine);
 
+	ce->lrc_desc &= ~GENMASK_ULL(47, 37);
 	if (ce->tag) {
 		/* Use a fixed tag for OA and friends */
 		ce->lrc_desc |= (u64)ce->tag << 32;
 	} else {
 		/* We don't need a strict matching tag, just different values */
-		ce->lrc_desc &= ~GENMASK_ULL(47, 37);
 		ce->lrc_desc |=
 			(u64)(++engine->context_tag % NUM_CONTEXT_TAG) <<
 			GEN11_SW_CTX_ID_SHIFT;

drivers/gpu/drm/i915/i915_perf.c

@@ -1323,7 +1323,13 @@ static int oa_get_render_ctx_id(struct i915_perf_stream *stream)
 	case 12: {
 		stream->specific_ctx_id_mask =
 			((1U << GEN11_SW_CTX_ID_WIDTH) - 1) << (GEN11_SW_CTX_ID_SHIFT - 32);
-		stream->specific_ctx_id = stream->specific_ctx_id_mask;
+		/*
+		 * Pick an unused context id
+		 * 0 - (NUM_CONTEXT_TAG - 1) are used by other contexts
+		 * GEN12_MAX_CONTEXT_HW_ID (0x7ff) is used by idle context
+		 */
+		stream->specific_ctx_id = (GEN12_MAX_CONTEXT_HW_ID - 1) << (GEN11_SW_CTX_ID_SHIFT - 32);
+		BUILD_BUG_ON((GEN12_MAX_CONTEXT_HW_ID - 1) < NUM_CONTEXT_TAG);
 		break;
 	}
 
@@ -1331,7 +1337,7 @@ static int oa_get_render_ctx_id(struct i915_perf_stream *stream)
 		MISSING_CASE(INTEL_GEN(ce->engine->i915));
 	}
 
-	ce->tag = stream->specific_ctx_id_mask;
+	ce->tag = stream->specific_ctx_id;
 
 	DRM_DEBUG_DRIVER("filtering on ctx_id=0x%x ctx_id_mask=0x%x\n",
 			 stream->specific_ctx_id,