Commit 63a81674 authored by Sai Praneeth Prakhya's avatar Sai Praneeth Prakhya Committed by Will Deacon
Browse files

iommu: Document usage of "/sys/kernel/iommu_groups/<grp_id>/type" file 



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.

Signed-off-by: default avatarSai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Signed-off-by: default avatarLu Baolu <baolu.lu@linux.intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Sohil Mehta <sohil.mehta@intel.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Link: https://lore.kernel.org/r/20201124130604.2912899-5-baolu.lu@linux.intel.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 0b8a96a3

Documentation/ABI/testing/sysfs-kernel-iommu_groups

+29 −0
Original line number Diff line number Diff line
@@ -33,3 +33,32 @@ 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.



What:		/sys/kernel/iommu_groups/<grp_id>/type

Date:		November 2020

KernelVersion:	v5.11

Contact:	Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>

Description:	/sys/kernel/iommu_groups/<grp_id>/type shows the type of default

		domain in use by iommu for this group. See include/linux/iommu.h

		for possible values. A privileged user could request kernel to

		change the group type by writing to this file. Presently, only

		three types of request 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.

		Note:

		-----

		The default domain type of a group may 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 users must unbind the appropriate driver before

		   changing the default domain type.

		Caution:

		--------

		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 users might

		need to reboot the machine to get it to normal state). So, it's

		expected that the users understand what they're doing.

CRA Git | Maintained and supported by SUSTech CRA and CCSE