iommu: Add generic_single_device_group()

This implements the common pattern seen in drivers of a single iommu_group
for the entire iommu driver instance. Implement this in core code so the
drivers that want this can select it from their ops.
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/2-v1-c869a95191f2+5e8-iommu_single_grp_jgg@nvidia.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -292,6 +292,10 @@ void iommu_device_unregister(struct iommu_device *iommu)
 	spin_lock(&iommu_device_lock);
 	list_del(&iommu->list);
 	spin_unlock(&iommu_device_lock);
+
+	/* Pairs with the alloc in generic_single_device_group() */
+	iommu_group_put(iommu->singleton_group);
+	iommu->singleton_group = NULL;
 }
 EXPORT_SYMBOL_GPL(iommu_device_unregister);
 
@@ -406,6 +410,7 @@ static int iommu_init_device(struct device *dev, const struct iommu_ops *ops)
 		ret = PTR_ERR(iommu_dev);
 		goto err_module_put;
 	}
+	dev->iommu->iommu_dev = iommu_dev;
 
 	ret = iommu_device_link(iommu_dev, dev);
 	if (ret)
@@ -420,7 +425,6 @@ static int iommu_init_device(struct device *dev, const struct iommu_ops *ops)
 	}
 	dev->iommu_group = group;
 
-	dev->iommu->iommu_dev = iommu_dev;
 	dev->iommu->max_pasids = dev_iommu_get_max_pasids(dev);
 	if (ops->is_attach_deferred)
 		dev->iommu->attach_deferred = ops->is_attach_deferred(dev);
@@ -434,6 +438,7 @@ static int iommu_init_device(struct device *dev, const struct iommu_ops *ops)
 err_module_put:
 	module_put(ops->owner);
 err_free:
+	dev->iommu->iommu_dev = NULL;
 	dev_iommu_free(dev);
 	return ret;
 }
@@ -1637,6 +1642,27 @@ struct iommu_group *generic_device_group(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(generic_device_group);
 
+/*
+ * Generic device_group call-back function. It just allocates one
+ * iommu-group per iommu driver instance shared by every device
+ * probed by that iommu driver.
+ */
+struct iommu_group *generic_single_device_group(struct device *dev)
+{
+	struct iommu_device *iommu = dev->iommu->iommu_dev;
+
+	if (!iommu->singleton_group) {
+		struct iommu_group *group;
+
+		group = iommu_group_alloc();
+		if (IS_ERR(group))
+			return group;
+		iommu->singleton_group = group;
+	}
+	return iommu_group_ref_get(iommu->singleton_group);
+}
+EXPORT_SYMBOL_GPL(generic_single_device_group);
+
 /*
  * Use standard PCI bus topology, isolation features, and DMA alias quirks
  * to find or create an IOMMU group for a device.

include/linux/iommu.h

@@ -378,6 +378,7 @@ struct iommu_domain_ops {
  * @list: Used by the iommu-core to keep a list of registered iommus
  * @ops: iommu-ops for talking to this iommu
  * @dev: struct device for sysfs handling
+ * @singleton_group: Used internally for drivers that have only one group
  * @max_pasids: number of supported PASIDs
  */
 struct iommu_device {
@@ -385,6 +386,7 @@ struct iommu_device {
 	const struct iommu_ops *ops;
 	struct fwnode_handle *fwnode;
 	struct device *dev;
+	struct iommu_group *singleton_group;
 	u32 max_pasids;
 };
 
@@ -648,6 +650,7 @@ extern struct iommu_group *pci_device_group(struct device *dev);
 extern struct iommu_group *generic_device_group(struct device *dev);
 /* FSL-MC device grouping function */
 struct iommu_group *fsl_mc_device_group(struct device *dev);
+extern struct iommu_group *generic_single_device_group(struct device *dev);
 
 /**
  * struct iommu_fwspec - per-device IOMMU instance data