drm/xe: Avoid any races around ccs_mode update

Ensure that there are no drm clients when changing CCS mode.
Allow exec_queue creation only with enabled CCS engines.

v2: Rebase
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_device.c

@@ -73,6 +73,10 @@ static int xe_file_open(struct drm_device *dev, struct drm_file *file)
 	mutex_init(&xef->exec_queue.lock);
 	xa_init_flags(&xef->exec_queue.xa, XA_FLAGS_ALLOC1);
 
+	spin_lock(&xe->clients.lock);
+	xe->clients.count++;
+	spin_unlock(&xe->clients.lock);
+
 	file->driver_priv = xef;
 	return 0;
 }
@@ -105,6 +109,10 @@ static void xe_file_close(struct drm_device *dev, struct drm_file *file)
 	xa_destroy(&xef->vm.xa);
 	mutex_destroy(&xef->vm.lock);
 
+	spin_lock(&xe->clients.lock);
+	xe->clients.count--;
+	spin_unlock(&xe->clients.lock);
+
 	xe_drm_client_put(xef->client);
 	kfree(xef);
 }
@@ -225,6 +233,7 @@ struct xe_device *xe_device_create(struct pci_dev *pdev,
 	xe->info.force_execlist = xe_modparam.force_execlist;
 
 	spin_lock_init(&xe->irq.lock);
+	spin_lock_init(&xe->clients.lock);
 
 	init_waitqueue_head(&xe->ufence_wq);
 

drivers/gpu/drm/xe/xe_device_types.h

@@ -310,6 +310,15 @@ struct xe_device {
 		enum xe_sriov_mode __mode;
 	} sriov;
 
+	/** @clients: drm clients info */
+	struct {
+		/** @lock: Protects drm clients info */
+		spinlock_t lock;
+
+		/** @count: number of drm clients */
+		u64 count;
+	} clients;
+
 	/** @usm: unified memory state */
 	struct {
 		/** @asid: convert a ASID to VM */

drivers/gpu/drm/xe/xe_gt_ccs_mode.c

@@ -105,6 +105,7 @@ ccs_mode_store(struct device *kdev, struct device_attribute *attr,
 	       const char *buff, size_t count)
 {
 	struct xe_gt *gt = kobj_to_gt(&kdev->kobj);
+	struct xe_device *xe = gt_to_xe(gt);
 	u32 num_engines, num_slices;
 	int ret;
 
@@ -123,12 +124,21 @@ ccs_mode_store(struct device *kdev, struct device_attribute *attr,
 		return -EINVAL;
 	}
 
+	/* CCS mode can only be updated when there are no drm clients */
+	spin_lock(&xe->clients.lock);
+	if (xe->clients.count) {
+		spin_unlock(&xe->clients.lock);
+		return -EBUSY;
+	}
+
 	if (gt->ccs_mode != num_engines) {
 		xe_gt_info(gt, "Setting compute mode to %d\n", num_engines);
 		gt->ccs_mode = num_engines;
 		xe_gt_reset_async(gt);
 	}
 
+	spin_unlock(&xe->clients.lock);
+
 	return count;
 }