[PATCH v2 2/2] drm/xe: Convert xe_user_fence to drm_user_fence

[Srinivasan Shanmugam]

Replace the open-coded user fence implementation in xe_sync.c with the
new common drm_user_fence helper.

struct xe_user_fence now embeds struct drm_user_fence as its base.
XE-specific fields (xe_device pointer for the ufence_wq wake-up,
userspace VA, expected value, signalled flag) remain in the wrapper.

The local user_fence_destroy/get/put/worker/kick_ufence/user_fence_cb
functions are removed. Their logic moves to xe_ufence_ops.worker and
xe_ufence_ops.destroy, which are called by drm_user_fence_work().

Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Simona Vetter <simona@xxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: intel-xe@xxxxxxxxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@xxxxxxx>
---
v2:
 - Remove unconditional dma_fence_put(fence) after
   drm_user_fence_add_callback() in xe_sync_entry_signal(). The fence
   reference is now consumed by drm_user_fence_add_callback() in all
   paths — transferred to the callback on success, released internally
   on the already-signaled and error paths. (Sashiko review)

 drivers/gpu/drm/xe/xe_sync.c       | 112 ++++++++++++-----------------
 drivers/gpu/drm/xe/xe_sync_types.h |   1 -
 2 files changed, 44 insertions(+), 69 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_sync.c b/drivers/gpu/drm/xe/xe_sync.c
index 37866768d64c..7549123f8486 100644
--- a/drivers/gpu/drm/xe/xe_sync.c
+++ b/drivers/gpu/drm/xe/xe_sync.c
@@ -6,12 +6,11 @@
 #include "xe_sync.h"
 
 #include <linux/dma-fence-array.h>
-#include <linux/kthread.h>
-#include <linux/sched/mm.h>
 #include <linux/uaccess.h>
 
 #include <drm/drm_print.h>
 #include <drm/drm_syncobj.h>
+#include <drm/drm_user_fence.h>
 #include <uapi/drm/xe_drm.h>
 
 #include "xe_device.h"
@@ -19,36 +18,51 @@
 #include "xe_macros.h"
 #include "xe_sched_job_types.h"
 
+/*
+ * xe_user_fence wraps drm_user_fence with XE-specific fields.
+ * The drm_user_fence base handles MM borrowing and work-item lifetime.
+ */
 struct xe_user_fence {
-	struct xe_device *xe;
-	struct kref refcount;
-	struct dma_fence_cb cb;
-	struct work_struct worker;
-	struct mm_struct *mm;
-	u64 __user *addr;
-	u64 value;
-	int signalled;
+	struct drm_user_fence base;
+	struct xe_device     *xe;
+	u64 __user           *addr;
+	u64                   value;
+	int                   signalled;
 };
 
-static void user_fence_destroy(struct kref *kref)
+static void xe_ufence_worker(struct drm_user_fence *base, bool mm_ok)
 {
-	struct xe_user_fence *ufence = container_of(kref, struct xe_user_fence,
-						 refcount);
+	struct xe_user_fence *ufence = container_of(base, struct xe_user_fence, base);
 
-	mmdrop(ufence->mm);
-	kfree(ufence);
-}
+	/*
+	 * Mark signalled before waking waiters so UMD can safely reuse
+	 * the same ufence without hitting -EBUSY.
+	 */
+	WRITE_ONCE(ufence->signalled, 1);
 
-static void user_fence_get(struct xe_user_fence *ufence)
-{
-	kref_get(&ufence->refcount);
+	if (mm_ok) {
+		if (copy_to_user(ufence->addr, &ufence->value, sizeof(ufence->value)))
+			XE_WARN_ON("Copy to user failed");
+	} else {
+		drm_dbg(&ufence->xe->drm,
+			"mmget_not_zero() failed, ufence wasn't signaled\n");
+	}
+
+	wake_up_all(&ufence->xe->ufence_wq);
 }
 
-static void user_fence_put(struct xe_user_fence *ufence)
+static void xe_ufence_destroy(struct drm_user_fence *base)
 {
-	kref_put(&ufence->refcount, user_fence_destroy);
+	struct xe_user_fence *ufence = container_of(base, struct xe_user_fence, base);
+
+	kfree(ufence);
 }
 
+static const struct drm_user_fence_ops xe_ufence_ops = {
+	.worker  = xe_ufence_worker,
+	.destroy = xe_ufence_destroy,
+};
+
 static struct xe_user_fence *user_fence_create(struct xe_device *xe, u64 addr,
 					       u64 value)
 {
@@ -63,51 +77,22 @@ static struct xe_user_fence *user_fence_create(struct xe_device *xe, u64 addr,
 	if (!ufence)
 		return ERR_PTR(-ENOMEM);
 
-	ufence->xe = xe;
-	kref_init(&ufence->refcount);
-	ufence->addr = ptr;
+	ufence->xe    = xe;
+	ufence->addr  = ptr;
 	ufence->value = value;
-	ufence->mm = current->mm;
-	mmgrab(ufence->mm);
+	drm_user_fence_init(&ufence->base, xe->ordered_wq, &xe_ufence_ops);
 
 	return ufence;
 }
 
-static void user_fence_worker(struct work_struct *w)
-{
-	struct xe_user_fence *ufence = container_of(w, struct xe_user_fence, worker);
-
-	WRITE_ONCE(ufence->signalled, 1);
-	if (mmget_not_zero(ufence->mm)) {
-		kthread_use_mm(ufence->mm);
-		if (copy_to_user(ufence->addr, &ufence->value, sizeof(ufence->value)))
-			XE_WARN_ON("Copy to user failed");
-		kthread_unuse_mm(ufence->mm);
-		mmput(ufence->mm);
-	} else {
-		drm_dbg(&ufence->xe->drm, "mmget_not_zero() failed, ufence wasn't signaled\n");
-	}
-
-	/*
-	 * Wake up waiters only after updating the ufence state, allowing the UMD
-	 * to safely reuse the same ufence without encountering -EBUSY errors.
-	 */
-	wake_up_all(&ufence->xe->ufence_wq);
-	user_fence_put(ufence);
-}
-
-static void kick_ufence(struct xe_user_fence *ufence, struct dma_fence *fence)
+static void user_fence_get(struct xe_user_fence *ufence)
 {
-	INIT_WORK(&ufence->worker, user_fence_worker);
-	queue_work(ufence->xe->ordered_wq, &ufence->worker);
-	dma_fence_put(fence);
+	drm_user_fence_get(&ufence->base);
 }
 
-static void user_fence_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
+static void user_fence_put(struct xe_user_fence *ufence)
 {
-	struct xe_user_fence *ufence = container_of(cb, struct xe_user_fence, cb);
-
-	kick_ufence(ufence, fence);
+	drm_user_fence_put(&ufence->base);
 }
 
 int xe_sync_entry_parse(struct xe_device *xe, struct xe_file *xef,
@@ -282,24 +267,15 @@ void xe_sync_entry_signal(struct xe_sync_entry *sync, struct dma_fence *fence)
 	} else if (sync->syncobj) {
 		drm_syncobj_replace_fence(sync->syncobj, fence);
 	} else if (sync->ufence) {
-		int err;
-
 		drm_syncobj_add_point(sync->ufence_syncobj,
 				      sync->ufence_chain_fence,
 				      fence, sync->ufence_timeline_value);
 		sync->ufence_chain_fence = NULL;
 
 		fence = drm_syncobj_fence_get(sync->ufence_syncobj);
-		user_fence_get(sync->ufence);
-		err = dma_fence_add_callback(fence, &sync->ufence->cb,
-					     user_fence_cb);
-		if (err == -ENOENT) {
-			kick_ufence(sync->ufence, fence);
-		} else if (err) {
+		if (drm_user_fence_add_callback(&sync->ufence->base, fence))
 			XE_WARN_ON("failed to add user fence");
-			user_fence_put(sync->ufence);
-			dma_fence_put(fence);
-		}
+		/* fence ref consumed by drm_user_fence_add_callback */
 	}
 }
 
diff --git a/drivers/gpu/drm/xe/xe_sync_types.h b/drivers/gpu/drm/xe/xe_sync_types.h
index b88f1833e28c..67048199b070 100644
--- a/drivers/gpu/drm/xe/xe_sync_types.h
+++ b/drivers/gpu/drm/xe/xe_sync_types.h
@@ -12,7 +12,6 @@ struct drm_syncobj;
 struct dma_fence;
 struct dma_fence_chain;
 struct drm_xe_sync;
-struct user_fence;
 
 struct xe_sync_entry {
 	struct drm_syncobj *syncobj;
-- 
2.34.1