[PATCH v2] drm/i915/gt: Hold a wakeref for the active VM

Andrzej Hajda
2023-03-31T14:16:58Z

From: Chris Wilson <chris@chris-wilson.co.uk>

There may be a disconnect between the GT used by the engine and the GT
used for the VM, requiring us to hold a wakeref on both while the GPU is
active with this request.

v2: added explanation to __queue_and_release_pm

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[ahajda: removed not-yet-upstremed wakeref tracking bits]
Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
---
Changes in v2:
- Link to v1: https://lore.kernel.org/r/20230330-hold_wakeref_for_active_vm-v1-1-baca712692f6@intel.com
---
drivers/gpu/drm/i915/gt/intel_context.h | 15 +++++++++++----
drivers/gpu/drm/i915/gt/intel_engine_pm.c | 9 +++++++++
2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
index 0a8d553da3f439..48f888c3da083b 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.h
+++ b/drivers/gpu/drm/i915/gt/intel_context.h
@@ -14,6 +14,7 @@
#include "i915_drv.h"
#include "intel_context_types.h"
#include "intel_engine_types.h"
+#include "intel_gt_pm.h"
#include "intel_ring_types.h"
#include "intel_timeline_types.h"
#include "i915_trace.h"
@@ -207,8 +208,11 @@ void intel_context_exit_engine(struct intel_context *ce);
static inline void intel_context_enter(struct intel_context *ce)
{
lockdep_assert_held(&ce->timeline->mutex);
- if (!ce->active_count++)
- ce->ops->enter(ce);
+ if (ce->active_count++)
+ return;
+
+ ce->ops->enter(ce);
+ intel_gt_pm_get(ce->vm->gt);
}

static inline void intel_context_mark_active(struct intel_context *ce)
@@ -222,8 +226,11 @@ static inline void intel_context_exit(struct intel_context *ce)
{
lockdep_assert_held(&ce->timeline->mutex);
GEM_BUG_ON(!ce->active_count);
- if (!--ce->active_count)
- ce->ops->exit(ce);
+ if (--ce->active_count)
+ return;
+
+ intel_gt_pm_put_async(ce->vm->gt);
+ ce->ops->exit(ce);
}

static inline struct intel_context *intel_context_get(struct intel_context *ce)
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
index e971b153fda976..ee531a5c142c77 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
@@ -114,6 +114,15 @@ __queue_and_release_pm(struct i915_request *rq,

ENGINE_TRACE(engine, "parking\n");

+ /*
+ * Open coded one half of intel_context_enter, which we have to omit
+ * here (see the large comment below) and because the other part must
+ * not be called due constructing directly with __i915_request_create
+ * which increments active count via intel_context_mark_active.
+ */
+ GEM_BUG_ON(rq->context->active_count != 1);
+ __intel_gt_pm_get(engine->gt);
+
/*
* We have to serialise all potential retirement paths with our
* submission, as we don't want to underflow either the

---
base-commit: 3385d6482cd60f2a0bbb0fa97b70ae7dbba4f95c
change-id: 20230330-hold_wakeref_for_active_vm-7f013a449ef3

Best regards,
--
Andrzej Hajda <andrzej.hajda@intel.com>