iommu: Add iommu_paging_domain_alloc() interface

Commit <17de3f5f> ("iommu: Retire bus ops") removes iommu ops from
bus. The iommu subsystem no longer relies on bus for operations. So the
bus parameter in iommu_domain_alloc() is no longer relevant.

Add a new interface named iommu_paging_domain_alloc(), which explicitly
indicates the allocation of a paging domain for DMA managed by a kernel
driver. The new interface takes a device pointer as its parameter, that
better aligns with the current iommu subsystem.
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Link: https://lore.kernel.org/r/20240610085555.88197-2-baolu.lu@linux.intel.comSigned-off-by: Will Deacon <will@kernel.org>

drivers/iommu/iommu.c

@@ -2016,6 +2016,10 @@ static int __iommu_domain_alloc_dev(struct device *dev, void *data)
 	return 0;
 }
 
+/*
+ * The iommu ops in bus has been retired. Do not use this interface in
+ * new drivers.
+ */
 struct iommu_domain *iommu_domain_alloc(const struct bus_type *bus)
 {
 	const struct iommu_ops *ops = NULL;
@@ -2032,6 +2036,22 @@ struct iommu_domain *iommu_domain_alloc(const struct bus_type *bus)
 }
 EXPORT_SYMBOL_GPL(iommu_domain_alloc);
 
+/**
+ * iommu_paging_domain_alloc() - Allocate a paging domain
+ * @dev: device for which the domain is allocated
+ *
+ * Allocate a paging domain which will be managed by a kernel driver. Return
+ * allocated domain if successful, or a ERR pointer for failure.
+ */
+struct iommu_domain *iommu_paging_domain_alloc(struct device *dev)
+{
+	if (!dev_has_iommu(dev))
+		return ERR_PTR(-ENODEV);
+
+	return __iommu_domain_alloc(dev_iommu_ops(dev), dev, IOMMU_DOMAIN_UNMANAGED);
+}
+EXPORT_SYMBOL_GPL(iommu_paging_domain_alloc);
+
 void iommu_domain_free(struct iommu_domain *domain)
 {
 	if (domain->type == IOMMU_DOMAIN_SVA)

include/linux/iommu.h

@@ -780,6 +780,7 @@ extern bool iommu_present(const struct bus_type *bus);
 extern bool device_iommu_capable(struct device *dev, enum iommu_cap cap);
 extern bool iommu_group_has_isolated_msi(struct iommu_group *group);
 extern struct iommu_domain *iommu_domain_alloc(const struct bus_type *bus);
+struct iommu_domain *iommu_paging_domain_alloc(struct device *dev);
 extern void iommu_domain_free(struct iommu_domain *domain);
 extern int iommu_attach_device(struct iommu_domain *domain,
 			       struct device *dev);
@@ -1086,6 +1087,11 @@ static inline struct iommu_domain *iommu_domain_alloc(const struct bus_type *bus
 	return NULL;
 }
 
+static inline struct iommu_domain *iommu_paging_domain_alloc(struct device *dev)
+{
+	return ERR_PTR(-ENODEV);
+}
+
 static inline void iommu_domain_free(struct iommu_domain *domain)
 {
 }