[Intel-xe] [RFC v3 2/2] drm/xe: Avoid any races around ccs_mode update

[Niranjana Vishwanathapura]

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

Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>
---
 drivers/gpu/drm/xe/xe_device.c       | 9 +++++++++
 drivers/gpu/drm/xe/xe_device_types.h | 9 +++++++++
 drivers/gpu/drm/xe/xe_gt_sysfs.c     | 9 +++++++++
 3 files changed, 27 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index 1202f8007f79..27e6f0bf423e 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/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->ccs_mode.lock);
+	xe->ccs_mode.num_drm_clients++;
+	spin_unlock(&xe->ccs_mode.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->ccs_mode.lock);
+	xe->ccs_mode.num_drm_clients--;
+	spin_unlock(&xe->ccs_mode.lock);
+
 	xe_drm_client_put(xef->client);
 	kfree(xef);
 }
@@ -228,6 +236,7 @@ struct xe_device *xe_device_create(struct pci_dev *pdev,
 	xe->info.force_execlist = force_execlist;
 
 	spin_lock_init(&xe->irq.lock);
+	spin_lock_init(&xe->ccs_mode.lock);
 
 	init_waitqueue_head(&xe->ufence_wq);
 
diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
index be11cadccbd4..3382281146aa 100644
--- a/drivers/gpu/drm/xe/xe_device_types.h
+++ b/drivers/gpu/drm/xe/xe_device_types.h
@@ -297,6 +297,15 @@ struct xe_device {
 		struct ttm_resource_manager sys_mgr;
 	} mem;
 
+	/** @ccs_mode: ccs mode */
+	struct {
+		/** @lock: Ensure there are no clients while setting ccs_mode */
+		spinlock_t lock;
+
+		/** @num_drm_clients: number of drm clients */
+		u64 num_drm_clients;
+	} ccs_mode;
+
 	/** @usm: unified memory state */
 	struct {
 		/** @asid: convert a ASID to VM */
diff --git a/drivers/gpu/drm/xe/xe_gt_sysfs.c b/drivers/gpu/drm/xe/xe_gt_sysfs.c
index e53221c2894f..c4779efd65b4 100644
--- a/drivers/gpu/drm/xe/xe_gt_sysfs.c
+++ b/drivers/gpu/drm/xe/xe_gt_sysfs.c
@@ -48,6 +48,7 @@ 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;
 
@@ -66,12 +67,20 @@ ccs_mode_store(struct device *kdev, struct device_attribute *attr,
 		return -EINVAL;
 	}
 
+	spin_lock(&xe->ccs_mode.lock);
+	if (xe->ccs_mode.num_drm_clients) {
+		spin_unlock(&xe->ccs_mode.lock);
+		return -EBUSY;
+	}
+
 	if (gt->ccs.num_engines != num_engines) {
 		xe_gt_info(gt, "Setting compute mode to %d\n", num_engines);
 		gt->ccs.num_engines = num_engines;
 		xe_gt_reset_async(gt);
 	}
 
+	spin_unlock(&xe->ccs_mode.lock);
+
 	return count;
 }
 
-- 
2.21.0.rc0.32.g243a4c7e27