[Intel-xe] [PATCH v2 3/3] 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.

v2: Rebase

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_ccs_mode.c  | 10 ++++++++++
 3 files changed, 28 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index 54202623e255..c7134d377b4c 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -72,6 +72,10 @@ 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;
 }
@@ -104,6 +108,10 @@ 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);
 }
@@ -226,6 +234,7 @@ 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);
 
diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
index 2712905c7a91..12cb1caacda8 100644
--- a/drivers/gpu/drm/xe/xe_device_types.h
+++ b/drivers/gpu/drm/xe/xe_device_types.h
@@ -306,6 +306,15 @@ 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 */
diff --git a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
index 0ad97383aedd..303ffb0761d8 100644
--- a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
+++ b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
@@ -90,6 +90,7 @@ 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;
 
@@ -108,12 +109,21 @@ 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 != num_engines) {
 		xe_gt_info(gt, "Setting compute mode to %d\n", num_engines);
 		gt->ccs_mode.num_engines = num_engines;
 		xe_gt_reset_async(gt);
 	}
 
+	spin_unlock(&xe->clients.lock);
+
 	return count;
 }
 
-- 
2.21.0.rc0.32.g243a4c7e27