[PATCH 5/5] drm/i915: switch intel_wakeref_t underlying type to struct ref_tracker *

[Jani Nikula]

For intel_wakeref_t, opaque is reasonable, but disguising the underlying
struct ref_tracker * as an unsigned long is not so great. Update the
typedef to remove one level of disguise.

Although the kernel coding style strongly discourages pointer typedefs,
it's a better alternative, and an incremental improvement on the status
quo. It provides much better type safety than an unsigned long could,
and prevents passing magic -1 instead of INTEL_WAKEREF_DEF. Moreover, it
provides a gradual path for replacing intel_wakeref_t with struct
ref_tracker * if desired.

As an extra safety measure, check for error pointers in
intel_ref_tracker_free() before passing them on to ref_tracker_free(),
to catch any mistakes with mock gt special wakeref value.

Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_gt_pm.h            |  2 +-
 drivers/gpu/drm/i915/intel_wakeref.h             | 16 +++++++++-------
 .../drm/xe/compat-i915-headers/intel_wakeref.h   |  4 ++--
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.h b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
index fef8d5d288f8..dcbfc09194b7 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_pm.h
+++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
@@ -105,7 +105,7 @@ int intel_gt_runtime_resume(struct intel_gt *gt);
 
 ktime_t intel_gt_get_awake_time(const struct intel_gt *gt);
 
-#define INTEL_WAKEREF_MOCK_GT ((intel_wakeref_t)-ENODEV)
+#define INTEL_WAKEREF_MOCK_GT ERR_PTR(-ENODEV)
 
 static inline bool is_mock_gt(const struct intel_gt *gt)
 {
diff --git a/drivers/gpu/drm/i915/intel_wakeref.h b/drivers/gpu/drm/i915/intel_wakeref.h
index 3944587a5e78..48836ef52d40 100644
--- a/drivers/gpu/drm/i915/intel_wakeref.h
+++ b/drivers/gpu/drm/i915/intel_wakeref.h
@@ -21,7 +21,7 @@
 #include <linux/timer.h>
 #include <linux/workqueue.h>
 
-typedef unsigned long intel_wakeref_t;
+typedef struct ref_tracker *intel_wakeref_t;
 
 #define INTEL_REFTRACK_DEAD_COUNT 16
 #define INTEL_REFTRACK_PRINT_LIMIT 16
@@ -273,7 +273,7 @@ __intel_wakeref_defer_park(struct intel_wakeref *wf)
  */
 int intel_wakeref_wait_for_idle(struct intel_wakeref *wf);
 
-#define INTEL_WAKEREF_DEF ((intel_wakeref_t)(-1))
+#define INTEL_WAKEREF_DEF ERR_PTR(-ENOENT)
 
 static inline intel_wakeref_t intel_ref_tracker_alloc(struct ref_tracker_dir *dir)
 {
@@ -281,17 +281,19 @@ static inline intel_wakeref_t intel_ref_tracker_alloc(struct ref_tracker_dir *di
 
 	ref_tracker_alloc(dir, &user, GFP_NOWAIT);
 
-	return (intel_wakeref_t)user ?: INTEL_WAKEREF_DEF;
+	return user ?: INTEL_WAKEREF_DEF;
 }
 
 static inline void intel_ref_tracker_free(struct ref_tracker_dir *dir,
-					  intel_wakeref_t handle)
+					  intel_wakeref_t wakeref)
 {
-	struct ref_tracker *user;
+	if (wakeref == INTEL_WAKEREF_DEF)
+		wakeref = NULL;
 
-	user = (handle == INTEL_WAKEREF_DEF) ? NULL : (void *)handle;
+	if (WARN_ON(IS_ERR(wakeref)))
+		return;
 
-	ref_tracker_free(dir, &user);
+	ref_tracker_free(dir, &wakeref);
 }
 
 void intel_ref_tracker_show(struct ref_tracker_dir *dir,
diff --git a/drivers/gpu/drm/xe/compat-i915-headers/intel_wakeref.h b/drivers/gpu/drm/xe/compat-i915-headers/intel_wakeref.h
index 5c139ba144a6..2a32faea9db5 100644
--- a/drivers/gpu/drm/xe/compat-i915-headers/intel_wakeref.h
+++ b/drivers/gpu/drm/xe/compat-i915-headers/intel_wakeref.h
@@ -5,6 +5,6 @@
 
 #include <linux/types.h>
 
-typedef unsigned long intel_wakeref_t;
+typedef struct ref_tracker *intel_wakeref_t;
 
-#define INTEL_WAKEREF_DEF ((intel_wakeref_t)(-1))
+#define INTEL_WAKEREF_DEF ERR_PTR(-ENOENT)
-- 
2.39.2