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 <h...@lst.de> Cc: Joerg Roedel <j...@8bytes.org> Cc: Ashok Raj <ashok....@intel.com> Cc: Will Deacon <will.dea...@arm.com> Cc: Lu Baolu <baolu...@linux.intel.com> Cc: Sohil Mehta <sohil.me...@intel.com> Cc: Robin Murphy <robin.mur...@arm.com> Cc: Jacob Pan <jacob.jun....@linux.intel.com> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prak...@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..a498daffeb0c 100644 --- a/Documentation/ABI/testing/sysfs-kernel-iommu_groups +++ b/Documentation/ABI/testing/sysfs-kernel-iommu_groups @@ -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. + +What: /sys/kernel/iommu_groups/<grp_id>/type +Date: June 2020 +KernelVersion: v5.8 +Contact: Sai Praneeth Prakhya <sai.praneeth.prak...@intel.com> +Description: Let 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. + Note: + ----- + 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. + 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 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. -- 2.19.1 _______________________________________________ iommu mailing list email@example.com https://lists.linuxfoundation.org/mailman/listinfo/iommu