[Intel-gfx] [PATCH 08/18] drm/i915/execlists: Wait for ELSP submission on restart

[Chris Wilson]

After a reset, we will ensure that there is at least one request
submitted to HW to ensure that a context is loaded for powersaving.
Let's wait for this submission via a tasklet to complete before we drop
our forcewake, ensuring the system is ready for rc6 before we let it
possible sleep.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.h  |  6 ++++++
 drivers/gpu/drm/i915/intel_lrc.c | 15 ++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
index 62ee4e385365..261da577829a 100644
--- a/drivers/gpu/drm/i915/i915_gem.h
+++ b/drivers/gpu/drm/i915/i915_gem.h
@@ -82,4 +82,10 @@ static inline void __tasklet_disable_sync_once(struct tasklet_struct *t)
 		tasklet_unlock_wait(t);
 }
 
+static inline void __tasklet_enable_sync_once(struct tasklet_struct *t)
+{
+	if (atomic_dec_return(&t->count) == 0)
+		tasklet_kill(t);
+}
+
 #endif /* __I915_GEM_H__ */
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index b3a5cfb7689f..f2fb48b1a7b7 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1877,6 +1877,8 @@ execlists_reset_prepare(struct intel_engine_cs *engine)
 
 	GEM_TRACE("%s\n", engine->name);
 
+	intel_uncore_forcewake_get(engine->i915, FORCEWAKE_ALL);
+
 	/*
 	 * Prevent request submission to the hardware until we have
 	 * completed the reset in i915_gem_reset_finish(). If a request
@@ -2007,7 +2009,18 @@ static void execlists_reset(struct intel_engine_cs *engine,
 
 static void execlists_reset_finish(struct intel_engine_cs *engine)
 {
-	tasklet_enable(&engine->execlists.tasklet);
+	/*
+	 * Flush the tasklet while we still have the forcewake to be sure
+	 * that it is not allowed to sleep before we restart and reload a
+	 * context.
+	 *
+	 * As before (with execlists_reset_prepare) we rely on the caller
+	 * serialising mutiple attempts to reset so that we know that we
+	 * are the only one manipulating tasklet state.
+	 */
+	__tasklet_enable_sync_once(&engine->execlists.tasklet);
+
+	intel_uncore_forcewake_put(engine->i915, FORCEWAKE_ALL);
 
 	GEM_TRACE("%s\n", engine->name);
 }
-- 
2.17.0