[PATCH 05/20] iommu: Allow an IDENTITY domain as the default_domain in ARM32

[Jason Gunthorpe]

Even though dma-iommu.c and CONFIG_ARM_DMA_USE_IOMMU do approximately the
same stuff, the way they relate to the IOMMU core is quiet different.

dma-iommu.c expects the core code to setup an UNMANAGED domain (of type
IOMMU_DOMAIN_DMA) and then configures itself to use that domain. This
becomes the default_domain for the group.

ARM_DMA_USE_IOMMU does not use the default_domain, instead it directly
allocates an UNMANAGED domain and operates it just like an external
driver. In this case group->default_domain is NULL.

Allow iommu drivers to specify a global static identity_domain and, if
present, automatically use this domain as the default_domain when in
ARM_DMA_USE_IOMMU mode.

This allows drivers that implemented default_domain == NULL as an IDENTITY
translation to trivially get a properly labeled non-NULL default_domain on
ARM32 configs.

With this arrangment when ARM_DMA_USE_IOMMU wants to disconnect from the
device the normal detach_domain flow will restore the IDENTITY domain as
the default domain. Overall this makes attach_dev() of the IDENTITY domain
called in the same places as detach_dev().

This effectively migrates these drivers to default_domain mode. For
drivers that support ARM64 they will gain support for the IDENTITY
translation mode for the dma_api and behave in a uniform way.

Drivers use this by setting ops->identity_domain to a static singleton
iommu_domain that implements the identity attach. If the core detects
ARM_DMA_USE_IOMMU mode then it automatically attaches the IDENTITY domain
during probe.

If the driver does not want to support dma_api with translation then it
always sets default_domain to the identity domain and even if IOMMU_DMA is
turned on it will not allow it to be used.

This allows removing the set_platform_dma_ops() from every remaining
driver.

Add the core support and convert rockchip to use it.

Signed-off-by: Jason Gunthorpe <jgg at nvidia.com>
---
 drivers/iommu/iommu.c          | 13 +++++++++++++
 drivers/iommu/rockchip-iommu.c | 19 +------------------
 include/linux/iommu.h          |  3 +++
 3 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index ba7f38630665b5..8b9af774de68f1 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1654,6 +1654,16 @@ iommu_group_alloc_default_domain(struct iommu_group *group, int req_type)
 	if (req_type)
 		return __iommu_group_alloc_default_domain(bus, group, req_type);
 
+	/*
+	 * ARM32 drivers supporting CONFIG_ARM_DMA_USE_IOMMU can declare an
+	 * identity_domain and it becomes their default domain. Later on
+	 * ARM_DMA_USE_IOMMU will install its UNMANAGED domain.
+	 */
+	if (IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU) &&
+	    bus->iommu_ops->identity_domain)
+		return __iommu_group_alloc_default_domain(
+			bus, group, IOMMU_DOMAIN_IDENTITY);
+
 	/* The driver gave no guidance on what type to use, try the default */
 	dom = __iommu_group_alloc_default_domain(bus, group, iommu_def_domain_type);
 	if (dom)
@@ -1923,6 +1933,9 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
 	if (bus == NULL || bus->iommu_ops == NULL)
 		return NULL;
 
+	if (type == IOMMU_DOMAIN_IDENTITY && bus->iommu_ops->identity_domain)
+		return bus->iommu_ops->identity_domain;
+
 	domain = bus->iommu_ops->domain_alloc(type);
 	if (!domain)
 		return NULL;
diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
index ea5a3088bb7e8a..9e1296a856ac4c 100644
--- a/drivers/iommu/rockchip-iommu.c
+++ b/drivers/iommu/rockchip-iommu.c
@@ -1017,13 +1017,8 @@ static int rk_iommu_identity_attach(struct iommu_domain *identity_domain,
 	return 0;
 }
 
-static void rk_iommu_identity_free(struct iommu_domain *domain)
-{
-}
-
 static struct iommu_domain_ops rk_identity_ops = {
 	.attach_dev = rk_iommu_identity_attach,
-	.free = rk_iommu_identity_free,
 };
 
 static struct iommu_domain rk_identity_domain = {
@@ -1031,13 +1026,6 @@ static struct iommu_domain rk_identity_domain = {
 	.ops = &rk_identity_ops,
 };
 
-#ifdef CONFIG_ARM
-static void rk_iommu_set_platform_dma(struct device *dev)
-{
-	WARN_ON(rk_iommu_identity_attach(&rk_identity_domain, dev));
-}
-#endif
-
 static int rk_iommu_attach_device(struct iommu_domain *domain,
 		struct device *dev)
 {
@@ -1087,9 +1075,6 @@ static struct iommu_domain *rk_iommu_domain_alloc(unsigned type)
 {
 	struct rk_iommu_domain *rk_domain;
 
-	if (type == IOMMU_DOMAIN_IDENTITY)
-		return &rk_identity_domain;
-
 	if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA)
 		return NULL;
 
@@ -1214,13 +1199,11 @@ static int rk_iommu_of_xlate(struct device *dev,
 }
 
 static const struct iommu_ops rk_iommu_ops = {
+	.identity_domain = &rk_identity_domain,
 	.domain_alloc = rk_iommu_domain_alloc,
 	.probe_device = rk_iommu_probe_device,
 	.release_device = rk_iommu_release_device,
 	.device_group = rk_iommu_device_group,
-#ifdef CONFIG_ARM
-	.set_platform_dma_ops = rk_iommu_set_platform_dma,
-#endif
 	.pgsize_bitmap = RK_IOMMU_PGSIZE_BITMAP,
 	.of_xlate = rk_iommu_of_xlate,
 	.default_domain_ops = &(const struct iommu_domain_ops) {
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ddcad3597c177b..427490b5736d40 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -253,6 +253,8 @@ struct iommu_iotlb_gather {
  * @pgsize_bitmap: bitmap of all possible supported page sizes
  * @owner: Driver module providing these ops
  * @default_domain: If not NULL this will always be set as the default domain.
+ * @identity_domain: An always available, always attachable identity
+ *                   translation.
  */
 struct iommu_ops {
 	bool (*capable)(struct device *dev, enum iommu_cap);
@@ -287,6 +289,7 @@ struct iommu_ops {
 	unsigned long pgsize_bitmap;
 	struct module *owner;
 	struct iommu_domain *default_domain;
+	struct iommu_domain *identity_domain;
 };
 
 /**
-- 
2.40.0