On 2021/9/27 17:42, Tian, Kevin wrote:

+int iommu_device_set_dma_hint(struct device *dev, enum dma_hint hint)
+{
+	struct iommu_group *group;
+	int ret;
+
+	group = iommu_group_get(dev);
+	/* not an iommu-probed device */
+	if (!group)
+		return 0;
+
+	mutex_lock(&group->mutex);
+	ret = __iommu_group_viable(group, hint);
+	mutex_unlock(&group->mutex);
+
+	iommu_group_put(group);
+	return ret;
+}

Conceptually, we could also move iommu_deferred_attach() from
iommu_dma_ops here to save unnecessary checks in the hot DMA API
paths?

Best regards,
baolu