drm/i915: Do a synchronous switch-to-kernel-context on idling

When the system idles, we switch to the kernel context as a defensive
measure (no users are harmed if the kernel context is lost). Currently,
we issue a switch to kernel context and then come back later to see if
the kernel context is still current and the system is idle. However,
if we are no longer privy to the runqueue ordering, then we have to
relax our assumptions about the logical state of the GPU and the only
way to ensure that the kernel context is currently loaded is by issuing
a request to run after all others, and wait for it to complete all while
preventing anyone else from issuing their own requests.

v2: Pull wedging into switch_to_kernel_context_sync() but only after
waiting (though only for the same short delay) for the active context to
finish.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190308093657.8640-1-chris@chris-wilson.co.uk

1 files changed, 2 insertions, 7 deletions

diff --git a/drivers/gpu/drm/i915/selftests/i915_gem.c b/drivers/gpu/drm/i915/selftests/i915_gem.c
index e77b7ed449ae..50bb7bbd26d3 100644
--- a/drivers/gpu/drm/i915/selftests/i915_gem.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem.c
@@ -84,14 +84,9 @@ static void simulate_hibernate(struct drm_i915_private *i915)
 
 static int pm_prepare(struct drm_i915_private *i915)
 {
-	int err = 0;
-
-	if (i915_gem_suspend(i915)) {
-		pr_err("i915_gem_suspend failed\n");
-		err = -EINVAL;
-	}
+	i915_gem_suspend(i915);
 
-	return err;
+	return 0;
 }
 
 static void pm_suspend(struct drm_i915_private *i915)