[RFC 01/11] iommu: Add iommu_domain_msi_geometry and DOMAIN_ATTR_MSI_GEOMETRY

[Eric Auger]

Introduce a new DOMAIN_ATTR_MSI_GEOMETRY domain attribute. It enables
to query the aperture of the IOVA window dedicated to MSIs.

x86 IOMMUs will typically expose an MSI aperture matching the 1MB
region [FEE0_0000h - FEF0_000h] corresponding to the APIC configuration
 space and no support for MSI translation.

On ARM, arm-smmu(-v3) translate MSIs. Aperture is not set indicating
MSI IOVA can live everywhere in the IOVA address space

Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
---
 drivers/iommu/iommu.c |  5 +++++
 include/linux/iommu.h | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 9a2f196..617cb2b 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1485,6 +1485,7 @@ int iommu_domain_get_attr(struct iommu_domain *domain,
 			  enum iommu_attr attr, void *data)
 {
 	struct iommu_domain_geometry *geometry;
+	struct iommu_domain_msi_geometry *msi_geometry;
 	bool *paging;
 	int ret = 0;
 	u32 *count;
@@ -1495,6 +1496,10 @@ int iommu_domain_get_attr(struct iommu_domain *domain,
 		*geometry = domain->geometry;
 
 		break;
+	case DOMAIN_ATTR_MSI_GEOMETRY:
+		msi_geometry  = data;
+		*msi_geometry = domain->msi_geometry;
+		break;
 	case DOMAIN_ATTR_PAGING:
 		paging  = data;
 		*paging = (domain->pgsize_bitmap != 0UL);
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 436dc21..ef6e047 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -52,6 +52,11 @@ struct iommu_domain_geometry {
 	bool force_aperture;       /* DMA only allowed in mappable range? */
 };
 
+struct iommu_domain_msi_geometry {
+	dma_addr_t aperture_start; /* First address usable for MSI IOVA     */
+	dma_addr_t aperture_end;   /* Last address usable for MSI IOVA      */
+};
+
 /* Domain feature flags */
 #define __IOMMU_DOMAIN_PAGING	(1U << 0)  /* Support for iommu_map/unmap */
 #define __IOMMU_DOMAIN_DMA_API	(1U << 1)  /* Domain for use in DMA-API
@@ -83,6 +88,7 @@ struct iommu_domain {
 	iommu_fault_handler_t handler;
 	void *handler_token;
 	struct iommu_domain_geometry geometry;
+	struct iommu_domain_msi_geometry msi_geometry;
 	void *iova_cookie;
 };
 
@@ -108,6 +114,7 @@ enum iommu_cap {
 
 enum iommu_attr {
 	DOMAIN_ATTR_GEOMETRY,
+	DOMAIN_ATTR_MSI_GEOMETRY,
 	DOMAIN_ATTR_PAGING,
 	DOMAIN_ATTR_WINDOWS,
 	DOMAIN_ATTR_FSL_PAMU_STASH,
@@ -352,6 +359,12 @@ int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
 void iommu_fwspec_free(struct device *dev);
 int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids);
 
+static inline bool iommu_domain_msi_aperture_valid(struct iommu_domain *domain)
+{
+	return (domain->msi_geometry.aperture_end >
+		domain->msi_geometry.aperture_start);
+}
+
 #else /* CONFIG_IOMMU_API */
 
 struct iommu_ops {};
-- 
1.9.1