Hi, On 2020/2/17 5:57, Sai Praneeth Prakhya wrote:
The default domain type of an iommu group can be changed using file "/sys/kernel/iommu_groups/<grp_id>/type". Hence, document it's usage and more importantly spell out it's 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 | 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..808a9507b281 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: February 2020 +KernelVersion: v5.6 +Contact: Sai Praneeth Prakhya <sai.praneeth.prak...@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
Let the users know the default domain type of the IOMMU group by reading this file. A privileged user could request to change it by writing to this file.
+ the group type by writing to this file. Presently, only three + types are supported + 1. DMA: All the DMA transactions from the devices in this group + are translated by the iommu. + 2. identity: All the DMA transactions from the devices in this + group are *not* translated by the iommu. + 3. auto: Kernel decides one among DMA/identity mode and hence + when the user reads the file he would never see "auto".
Just out of curiosity, when could a user reads "auto" from this file?
+ This is just a write only value. + Note: + ----- + A group type could be modified only when *all* the devices in
group's default domain type (not group type).
+ the group are not binded to any device driver. So, the user has
bound
+ to first unbind the appropriate drivers and then change the + default domain type. + Caution: + -------- + Unbinding a device driver will take away the drivers 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.
Best regards, baolu _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
