Commit adf5e516 authored by Robin Murphy's avatar Robin Murphy Committed by Will Deacon
Browse files

iommu: Better document the IOMMU_PRIV flag 



This is a fairly subtle thing - let's make sure it's described as
clearly as possible to avoid potential misunderstandings.

Signed-off-by: default avatarRobin Murphy <robin.murphy@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent c02ed2e7

include/linux/iommu.h

+7 −4
Original line number Diff line number Diff line
@@ -32,10 +32,13 @@ 
#define IOMMU_NOEXEC	(1 << 3)

#define IOMMU_MMIO	(1 << 4) /* e.g. things like MSI doorbells */

/*

 * This is to make the IOMMU API setup privileged

 * mapppings accessible by the master only at higher

 * privileged execution level and inaccessible at

 * less privileged levels.

 * Where the bus hardware includes a privilege level as part of its access type

 * markings, and certain devices are capable of issuing transactions marked as

 * either 'supervisor' or 'user', the IOMMU_PRIV flag requests that the other

 * given permission flags only apply to accesses at the higher privilege level,

 * and that unprivileged transactions should have as little access as possible.

 * This would usually imply the same permissions as kernel mappings on the CPU,

 * if the IOMMU page table format is equivalent.

 */

#define IOMMU_PRIV	(1 << 5)