Messages in this thread Patch in this message | | | From | Lu Baolu <> | Subject | [PATCH v10 4/4] iommu: Document usage of "/sys/kernel/iommu_groups/<grp_id>/type" file | Date | Tue, 24 Nov 2020 21:06:04 +0800 |
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From: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
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@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> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> --- .../ABI/testing/sysfs-kernel-iommu_groups | 29 +++++++++++++++++++ 1 file changed, 29 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-kernel-iommu_groups b/Documentation/ABI/testing/sysfs-kernel-iommu_groups index 017f5bc3920c..407b1628d7fd 100644 --- a/Documentation/ABI/testing/sysfs-kernel-iommu_groups +++ b/Documentation/ABI/testing/sysfs-kernel-iommu_groups @@ -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. -- 2.25.1
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