[PATCH v3 04/25] xen/arm: document dom0less

[Stefano Stabellini <sstabellini@kernel.org>]

Add a new document to provide information on how to use dom0less related
features and their current limitations.

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>

---
Changes in v3:
- add patch
---
 docs/misc/arm/dom0less | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 docs/misc/arm/dom0less

diff --git a/docs/misc/arm/dom0less b/docs/misc/arm/dom0less
new file mode 100644
index 0000000..ae5a8b1
--- /dev/null
+++ b/docs/misc/arm/dom0less
@@ -0,0 +1,47 @@
+Dom0less
+========
+
+"Dom0less" is a set of Xen features that enable the deployment of a Xen
+system without Dom0. Each feature can be used independently from the
+others, unless otherwise stated.
+
+Booting Multiple Domains from Device Tree
+=========================================
+
+This feature enables Xen to create a set of DomUs alongside Dom0 at boot
+time. Information about the DomUs to be created by Xen is passed to the
+hypervisor via Device Tree. Specifically, the existing Device Tree based
+Multiboot specification has been extended to allow for multiple domains
+to be passed to Xen. See docs/misc/arm/device-tree/booting.txt for more
+information about the Multiboot specification and how to use it.
+
+Instead of waiting for Dom0 to be fully booted and the Xen tools to
+become available, domains created by Xen this way are started in
+parallel to Dom0. Hence, their boot time is typically much shorter.
+
+Domains started by Xen at boot time currently have the following
+limitations:
+
+- they cannot be properly shutdown or rebooted using xl
+If one of them crashes, the whole platform should be rebooted.
+
+- some xl operations might not work as expected
+xl is meant to be used with domains that have been created by it. Using
+xl with domains started by Xen at boot might not work as expected.
+
+- the GIC version is the native version
+In absence of other information, the GIC version exposed to the domains
+started by Xen at boot is the same as the native GIC version.
+
+- no PV drivers
+There is no support for PV devices at the moment. All devices need to be
+statically assigned to guests.
+
+- vCPU pinning
+Pinning vCPUs of domains started by Xen at boot can be done from dom0,
+using `xl vcpu-pin' as usual. It is not currently possible to configure
+vCPU pinning for domains other than dom0 without dom0. However, the NULL
+scheduler (currently unsupported) can be selected by passing
+`sched=null' to the Xen command line. The NULL scheduler automatically
+assignes and pins vCPUs to pCPUs, but the vCPU-pCPU assignments cannot
+be configured.
-- 
1.9.1


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