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

[Chris Wilson]

Quoting Chris Wilson (2018-05-22 11:19:37)
> 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 

Pushed with corrections and review from Mika (on a later thread). Thanks,
-Chris
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[Intel-gfx] [PATCH] 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 
---
 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 5bf24cfc218c..878b081f2af9 100644
--- a/drivers/gpu/drm/i915/i915_gem.h
+++ b/drivers/gpu/drm/i915/i915_gem.h
@@ -79,4 +79,10 @@ 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(>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(>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(>execlists.tasklet);
+
+   intel_uncore_forcewake_put(engine->i915, FORCEWAKE_ALL);
 
GEM_TRACE("%s\n", engine->name);
 }
-- 
2.17.0

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