[PATCH V3 3/3] iommu: Document usage of "/sys/kernel/iommu_groups/<grp_id>/type" file
Sai Praneeth Prakhya
sai.praneeth.prakhya at intel.com
Thu May 28 19:24:03 UTC 2020
The default domain type of an iommu group can be changed by writing to
"/sys/kernel/iommu_groups/<grp_id>/type" file. Hence, document it's usage
and more importantly spell out its limitations.
Cc: Christoph Hellwig <hch at lst.de>
Cc: Joerg Roedel <joro at 8bytes.org>
Cc: Ashok Raj <ashok.raj at intel.com>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Lu Baolu <baolu.lu at linux.intel.com>
Cc: Sohil Mehta <sohil.mehta at intel.com>
Cc: Robin Murphy <robin.murphy at arm.com>
Cc: Jacob Pan <jacob.jun.pan at linux.intel.com>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya at intel.com>
.../ABI/testing/sysfs-kernel-iommu_groups | 30 +++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-kernel-iommu_groups b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
index 017f5bc3920c..d238fca4408f 100644
@@ -33,3 +33,33 @@ Description: In case an RMRR is used only by graphics or USB devices
it is now exposed as "direct-relaxable" instead of "direct".
In device assignment use case, for instance, those RMRR
are considered to be relaxable and safe.
+Date: June 2020
+Contact: Sai Praneeth Prakhya <sai.praneeth.prakhya at intel.com>
+Description: Lets the user know the type of default domain in use by iommu
+ for this group. A privileged user could request kernel to change
+ the group type by writing to this file. Presently, only three
+ types are supported
+ 1. DMA: All the DMA transactions from the device in this group
+ are translated by the iommu.
+ 2. identity: All the DMA transactions from the device in this
+ group are *not* translated by the iommu.
+ 3. auto: Change to the type the device was booted with. When the
+ user reads the file he would never see "auto". This is
+ just a write only value.
+ A group type could be modified only when
+ 1. The group has *only* one device
+ 2. The device in the group is not bound to any device driver.
+ So, the user must first unbind the appropriate driver and
+ then change the default domain type.
+ Unbinding a device driver will take away the driver's control
+ over the device and if done on devices that host root file
+ system could lead to catastrophic effects (the user might
+ need to reboot the machine to get it to normal state). So, it's
+ expected that the user understands what he is doing.
More information about the iommu