From: Vikram Garhwal <fnu.vik...@xilinx.com> Signed-off-by: Vikram Garhwal <fnu.vik...@xilinx.com> Signed-off-by: Stefano Stabellini <stefano.stabell...@xilinx.com> Signed-off-by: Henry Wang <xin.wa...@amd.com> --- docs/misc/arm/overlay.txt | 82 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 82 insertions(+) create mode 100644 docs/misc/arm/overlay.txt
diff --git a/docs/misc/arm/overlay.txt b/docs/misc/arm/overlay.txt new file mode 100644 index 0000000000..0a2dee951a --- /dev/null +++ b/docs/misc/arm/overlay.txt @@ -0,0 +1,82 @@ +# Device Tree Overlays support in Xen + +Xen experimentally supports dynamic device assignment to running +domains, i.e. adding/removing nodes (using .dtbo) to/from Xen device +tree, and attaching them to a running domain with given $domid. + +Dynamic node assignment works in two steps: + +## Add/Remove device tree overlay to/from Xen device tree + +1. Xen tools check the dtbo given and parse all other user provided arguments +2. Xen tools pass the dtbo to Xen hypervisor via hypercall. +3. Xen hypervisor applies/removes the dtbo to/from Xen device tree. + +## Attach device from the DT overlay to domain + +1. Xen tools check the dtbo given and parse all other user provided arguments +2. Xen tools pass the dtbo to Xen hypervisor via hypercall. +3. Xen hypervisor attach the device to the user-provided $domid by + mapping node resources in the DT overlay. + +# Examples + +Here are a few examples on how to use it. + +## Dom0 device add + +For assigning a device tree overlay to Dom0, user should firstly properly +prepare the DT overlay. More information about device tree overlays can be +found in [1]. Then, in Dom0, enter the following: + + (dom0) xl dt-overlay add overlay.dtbo + +This will allocate the devices mentioned in overlay.dtbo to Xen device tree. + +To assign the newly added device from the dtbo to Dom0: + + (dom0) xl dt-overlay attach overlay.dtbo 0 + +Next, if the user wants to add the same device tree overlay to dom0 +Linux, execute the following: + + (dom0) mkdir -p /sys/kernel/config/device-tree/overlays/new_overlay + (dom0) cat overlay.dtbo > /sys/kernel/config/device-tree/overlays/new_overlay/dtbo + +Finally if needed, the relevant Linux kernel drive can be loaded using: + + (dom0) modprobe module_name.ko + +## DomU device add/remove + +All the nodes in dtbo will be assigned to a domain; the user will need +to prepare the dtb for the domU. For example, the `interrupt-parent` +property of the DomU overlay should be changed to the Xen hardcoded +value `0xfde8`, and the xen,reg property should be added to specify the +address mappings. If xen,reg is not present, it is assumed 1:1 mapping. +Below assumes the properly written DomU dtbo is `overlay_domu.dtbo`. + +For new domains to be created, the user will need to create the DomU +with below properties properly configured in the xl config file: +- `iomem` +- `passthrough` (if IOMMU is needed) + +User will also need to modprobe the relevant drivers. For already +running domains, the user can use the xl dt-overlay attach command, +example: + + (dom0) xl dt-overlay add overlay.dtbo # If not executed before + (dom0) xl dt-overlay attach overlay.dtbo $domid + (dom0) xl console $domid # To access $domid console + +Next, if the user needs to modify/prepare the overlay.dtbo suitable for +the domU: + + (domU) mkdir -p /sys/kernel/config/device-tree/overlays/new_overlay + (domU) cat overlay_domu.dtbo > /sys/kernel/config/device-tree/overlays/new_overlay/dtbo + +Finally, if needed, the relevant Linux kernel drive can be probed: + + (domU) modprobe module_name.ko + +[1] https://www.kernel.org/doc/Documentation/devicetree/overlay-notes.txt -- 2.25.1
