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Vikram Garhwal
ac572152e5
Signed-off-by: Vikram Garhwal <fnu.vikram@xilinx.com> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com> Signed-off-by: Henry Wang <xin.wang2@amd.com> Reviewed-by: Julien Grall <jgrall@amazon.com>
83 lines
3.1 KiB
Plaintext
83 lines
3.1 KiB
Plaintext
# Device Tree Overlays support in Xen
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Xen experimentally supports dynamic device assignment to running
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domains, i.e. adding/removing nodes (using .dtbo) to/from Xen device
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tree, and attaching them to a running domain with given $domid.
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Dynamic node assignment works in two steps:
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## Add/Remove device tree overlay to/from Xen device tree
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1. Xen tools check the dtbo given and parse all other user provided arguments
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2. Xen tools pass the dtbo to Xen hypervisor via hypercall.
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3. Xen hypervisor applies/removes the dtbo to/from Xen device tree.
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## Attach device from the DT overlay to domain
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1. Xen tools check the dtbo given and parse all other user provided arguments
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2. Xen tools pass the dtbo to Xen hypervisor via hypercall.
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3. Xen hypervisor attach the device to the user-provided $domid by
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mapping node resources in the DT overlay.
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# Examples
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Here are a few examples on how to use it.
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## Dom0 device add
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For assigning a device tree overlay to Dom0, user should firstly properly
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prepare the DT overlay. More information about device tree overlays can be
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found in [1]. Then, in Dom0, enter the following:
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(dom0) xl dt-overlay add overlay.dtbo
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This will allocate the devices mentioned in overlay.dtbo to Xen device tree.
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To assign the newly added device from the dtbo to Dom0:
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(dom0) xl dt-overlay attach overlay.dtbo 0
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Next, if the user wants to add the same device tree overlay to dom0
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Linux, execute the following:
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(dom0) mkdir -p /sys/kernel/config/device-tree/overlays/new_overlay
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(dom0) cat overlay.dtbo > /sys/kernel/config/device-tree/overlays/new_overlay/dtbo
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Finally if needed, the relevant Linux kernel drive can be loaded using:
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(dom0) modprobe module_name.ko
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## DomU device add/remove
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All the nodes in dtbo will be assigned to one domain. The user will need
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to prepare a different dtbo for the domU. For example, the
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`interrupt-parent` property of the DomU overlay should be changed to the
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Xen hardcoded value `0xfde8` and the xen,reg property should be added to
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specify the address mappings. If the domain is not 1:1 mapped, xen,reg
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must be present. See the xen,reg format description in
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docs/misc/arm/passthrough.txt. Below assumes the properly written DomU
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dtbo is `overlay_domu.dtbo`.
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The user needs to set the `passthrough` property in the xl config file
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if you plan to use DT overlay and devices requiring an IOMMU.
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User will also need to modprobe the relevant drivers. For already
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running domains, the user can use the xl dt-overlay attach command,
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example:
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(dom0) xl dt-overlay add overlay.dtbo # If not executed before
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(dom0) xl dt-overlay attach overlay_domu.dtbo $domid
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(dom0) xl console $domid # To access $domid console
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Next, if the user needs to modify/prepare the overlay.dtbo suitable for
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the domU:
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(domU) mkdir -p /sys/kernel/config/device-tree/overlays/new_overlay
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(domU) cat overlay_domu.dtbo > /sys/kernel/config/device-tree/overlays/new_overlay/dtbo
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Finally, if needed, the relevant Linux kernel drive can be probed:
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(domU) modprobe module_name.ko
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[1] https://www.kernel.org/doc/Documentation/devicetree/overlay-notes.txt
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