Merge pull request #79 from johnelse/integrated-gpu-passthrough-revision3

Revision 3 of the integrated GPU passthrough proposal

Author: johnelse

features/futures/integrated-gpu-passthrough.md

@@ -2,7 +2,7 @@
 title: Integrated GPU passthrough support
 layout: default
 design_doc: true
-revision: 2
+revision: 3
 status: proposed
 ---
 
@@ -21,23 +21,38 @@ GPUs.
 Host Configuration
 ------------------
 
-A new PGPU field will be added:
+New fields will be added (both read-only):
 
 - `PGPU.dom0_access enum(enabled|disable_on_reboot|disabled|enable_on_reboot)`
+- `host.display enum(enabled|disable_on_reboot|disabled|enable_on_reboot)`
 
-as well as new API calls:
+as well as new API calls used to modify the state of these fields:
 
 - `PGPU.enable_dom0_access`
 - `PGPU.disable_dom0_access`
+- `host.enable_display`
+- `host.disable_display`
+
+Each of these API calls will return the new state of the field e.g. calling
+`host.disable_display` on a host with `display = enabled` will return
+`disable_on_reboot`.
 
 Disabling dom0 access will modify the xen commandline (using the xen-cmdline
 tool) such that dom0 will not be able to access the GPU on next boot.
 
-A state diagram for the field PGPU.dom0_access is shown below:
+Calling host.disable_display will modify the xen and dom0 commandlines such
+that neither will attempt to send console output to the system display device.
+
+A state diagram for the fields `PGPU.dom0_access` and `host.display` is shown
+below:
 
 ![host.integrated_GPU_passthrough flow diagram](integrated-gpu-passthrough.png)
 
-Note that when a client enables or disables dom0 access for a PGPU, the change
+While it is possible for these two fields to be modified independently, a
+client must disable both the host display and dom0 access to the system display
+device before that device can be passed through to a guest.
+
+Note that when a client enables or disables either of these fields, the change
 can be cancelled until the host is rebooted.
 
 Handling vga_arbiter
@@ -52,9 +67,17 @@ supported_VGPU_types field will be empty.
 However, the PGPU's supported_VGPU_types will be populated as normal if:
 
 1.  dom0 access to the GPU is disabled.
-2.  The vendor ID of the device is contained in a whitelist provided by xapi's
+2.  The host's display is disabled.
+3.  The vendor ID of the device is contained in a whitelist provided by xapi's
     config file.
 
+A read-only field will be added:
+
+- `PGPU.is_system_display_device bool`
+
+This will be true for a PGPU iff `/dev/vga_arbiter` reports the PGPU as the
+system display device for the host on which the PGPU is installed.
+
 Interfacing with xenopsd
 ------------------------