提交 adf5e516 编写于 作者: R Robin Murphy 提交者: Will Deacon

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: NRobin Murphy <robin.murphy@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
上级 c02ed2e7
......@@ -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)
......
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