i915/oa: Simplify updating contexts

We can remove the update-via-batch-buffer code path, which is basically an
effective duplicate of update-via-context-image path, if we notice that
after we have idled the GPU, we can update the context image even of the
kernel context directly. (Update-via-batch-buffer path existed only to
solve the problem of how to update the kernel context image.)

Only additional thing needed is to activate the edited configuration by
sending one empty request down the pipe. This accomplishes context restore
of the updated kernel context and so the OA configuration gets written out
to it's control registers.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180912152930.28237-1-tvrtko.ursulin@linux.intel.com

drivers/gpu/drm/i915/i915_perf.c

@@ -1679,107 +1679,6 @@ static void gen8_update_reg_state_unlocked(struct i915_gem_context *ctx,
 	}
 }
 
-/*
- * Same as gen8_update_reg_state_unlocked only through the batchbuffer. This
- * is only used by the kernel context.
- */
-static int gen8_emit_oa_config(struct i915_request *rq,
-			       const struct i915_oa_config *oa_config)
-{
-	struct drm_i915_private *dev_priv = rq->i915;
-	/* The MMIO offsets for Flex EU registers aren't contiguous */
-	u32 flex_mmio[] = {
-		i915_mmio_reg_offset(EU_PERF_CNTL0),
-		i915_mmio_reg_offset(EU_PERF_CNTL1),
-		i915_mmio_reg_offset(EU_PERF_CNTL2),
-		i915_mmio_reg_offset(EU_PERF_CNTL3),
-		i915_mmio_reg_offset(EU_PERF_CNTL4),
-		i915_mmio_reg_offset(EU_PERF_CNTL5),
-		i915_mmio_reg_offset(EU_PERF_CNTL6),
-	};
-	u32 *cs;
-	int i;
-
-	cs = intel_ring_begin(rq, ARRAY_SIZE(flex_mmio) * 2 + 4);
-	if (IS_ERR(cs))
-		return PTR_ERR(cs);
-
-	*cs++ = MI_LOAD_REGISTER_IMM(ARRAY_SIZE(flex_mmio) + 1);
-
-	*cs++ = i915_mmio_reg_offset(GEN8_OACTXCONTROL);
-	*cs++ = (dev_priv->perf.oa.period_exponent << GEN8_OA_TIMER_PERIOD_SHIFT) |
-		(dev_priv->perf.oa.periodic ? GEN8_OA_TIMER_ENABLE : 0) |
-		GEN8_OA_COUNTER_RESUME;
-
-	for (i = 0; i < ARRAY_SIZE(flex_mmio); i++) {
-		u32 mmio = flex_mmio[i];
-
-		/*
-		 * This arbitrary default will select the 'EU FPU0 Pipeline
-		 * Active' event. In the future it's anticipated that there
-		 * will be an explicit 'No Event' we can select, but not
-		 * yet...
-		 */
-		u32 value = 0;
-
-		if (oa_config) {
-			u32 j;
-
-			for (j = 0; j < oa_config->flex_regs_len; j++) {
-				if (i915_mmio_reg_offset(oa_config->flex_regs[j].addr) == mmio) {
-					value = oa_config->flex_regs[j].value;
-					break;
-				}
-			}
-		}
-
-		*cs++ = mmio;
-		*cs++ = value;
-	}
-
-	*cs++ = MI_NOOP;
-	intel_ring_advance(rq, cs);
-
-	return 0;
-}
-
-static int gen8_switch_to_updated_kernel_context(struct drm_i915_private *dev_priv,
-						 const struct i915_oa_config *oa_config)
-{
-	struct intel_engine_cs *engine = dev_priv->engine[RCS];
-	struct i915_timeline *timeline;
-	struct i915_request *rq;
-	int ret;
-
-	lockdep_assert_held(&dev_priv->drm.struct_mutex);
-
-	i915_retire_requests(dev_priv);
-
-	rq = i915_request_alloc(engine, dev_priv->kernel_context);
-	if (IS_ERR(rq))
-		return PTR_ERR(rq);
-
-	ret = gen8_emit_oa_config(rq, oa_config);
-	if (ret) {
-		i915_request_add(rq);
-		return ret;
-	}
-
-	/* Queue this switch after all other activity */
-	list_for_each_entry(timeline, &dev_priv->gt.timelines, link) {
-		struct i915_request *prev;
-
-		prev = i915_gem_active_raw(&timeline->last_request,
-					   &dev_priv->drm.struct_mutex);
-		if (prev)
-			i915_request_await_dma_fence(rq, &prev->fence);
-	}
-
-	i915_request_add(rq);
-
-	return 0;
-}
-
 /*
  * Manages updating the per-context aspects of the OA stream
  * configuration across all contexts.
@@ -1809,16 +1708,11 @@ static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv,
 {
 	struct intel_engine_cs *engine = dev_priv->engine[RCS];
 	struct i915_gem_context *ctx;
+	struct i915_request *rq;
 	int ret;
-	unsigned int wait_flags = I915_WAIT_LOCKED;
 
 	lockdep_assert_held(&dev_priv->drm.struct_mutex);
 
-	/* Switch away from any user context. */
-	ret = gen8_switch_to_updated_kernel_context(dev_priv, oa_config);
-	if (ret)
-		return ret;
-
 	/*
 	 * The OA register config is setup through the context image. This image
 	 * might be written to by the GPU on context switch (in particular on
@@ -1833,7 +1727,7 @@ static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv,
 	 * the GPU from any submitted work.
 	 */
 	ret = i915_gem_wait_for_idle(dev_priv,
-				     wait_flags,
+				     I915_WAIT_LOCKED,
 				     MAX_SCHEDULE_TIMEOUT);
 	if (ret)
 		return ret;
@@ -1859,7 +1753,17 @@ static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv,
 		i915_gem_object_unpin_map(ce->state->obj);
 	}
 
-	return ret;
+	/*
+	 * Apply the configuration by doing one context restore of the edited
+	 * context image.
+	 */
+	rq = i915_request_alloc(engine, dev_priv->kernel_context);
+	if (IS_ERR(rq))
+		return PTR_ERR(rq);
+
+	i915_request_add(rq);
+
+	return 0;
 }
 
 static int gen8_enable_metric_set(struct drm_i915_private *dev_priv,