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Re: [Xen-devel] [PATCH 5/5] xen/arm: add dom0less device assignment info to docs
Hi Stefano,
On 07/08/2019 22:01, Stefano Stabellini wrote:
On Tue, 15 Jan 2019, Julien Grall wrote:
On 1/3/19 10:07 PM, Stefano Stabellini wrote:
On Mon, 24 Dec 2018, Julien Grall wrote:
Hi Stefano,
On 12/5/18 5:28 PM, Stefano Stabellini wrote:
Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
---
docs/misc/arm/device-tree/booting.txt | 108
++++++++++++++++++++++++++++++++++
1 file changed, 108 insertions(+)
diff --git a/docs/misc/arm/device-tree/booting.txt
b/docs/misc/arm/device-tree/booting.txt
index 317a9e9..f5aaf8f 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -226,3 +226,111 @@ chosen {
};
};
};
+
+
+Device Assignment
+=================
+
+Device Assignment (Passthrough) is supported by adding another module,
+alongside the kernel and ramdisk, with the device tree fragment
+corresponding to the device node to assign to the guest.
+
+The dtb sub-node should have the following properties:
+
+- compatible
+
+ "multiboot,dtb"
I would prefer "multiboot,device-tree"
I renamed it
+
+- reg
+
+ Specifies the physical address of the device tree binary fragment
+ RAM and its length.
+
+As an example:
+
+ module@0xc000000 {
+ compatible = "multiboot,dtb", "multiboot,module";
+ reg = <0x0 0xc000000 0xffffff>;
+ };
+
+The DTB fragment (loaded in memory at 0xc000000 in the example above)
+should follow the convention explained in
docs/misc/arm/passthrough.txt.
+The DTB fragment will be added to the guest device tree, so that the
+guest kernel will be able to discover the device.
+
+In addition, the following properties for each device node in the
device
+tree fragment will be used for the device assignment setup:
+
+- reg
+
+ The reg property specifying the address and size of the device
memory.
+ The device memory will be automatically mapped to the guest domain
+ with a 1:1 mapping (pseudo-physical address == physical address).
As said in a previous patch, I don't think this is correct to impose 1:1.
The
user is neither in control of the HW memory map nor the Guest memory map.
So
not many people are going to be able to use it without hacking Xen.
Yes, I'll fix this (and a couple of other issues) by introducing a new
"xen,reg" property, instead of trying to reuse the existing reg
property.
+
+- interrupts
+
+ The interrupts property specifies the interrupt of the device. They
+ are automatically routed to the guest domain with virtual irqs ==
+ physical irqs.
+
+- interrupt-parent
+
+ It contains a reference to the interrupt controller node. It should
be
+ 65000, corresponding to GUEST_PHANDLE_GIC.
We managed to get away in the toolstack with this property. So why do you
need
it for the hypervisor? Furthermore, this would forbid to passthrough any
other
interrupt controller to the guest.
The toolstack does use GUEST_PHANDLE_GIC today for passthrough
interrupts, see tools/libxl/libxl_arm.c:make_root_properties and
docs/misc/arm/passthrough.txt:
* The interrupt-parent property will be added by the toolstack in the
root node;
You misunderstood my point here. The toolstack is adding the property for the
user. So why does you require the user to add this property for Dom0less case?
I did misunderstand. interrupt-parent came from the example I had at hand,
which had
already the property even if it is unnecessary. I comfirmed that it is
superflous and I am happy to remove it.
FYI dtc throws a warning if interrupt-parent is missing:
<stdout>: Warning (interrupts_property): Missing interrupt-parent for
/passthrough/ethernet@ff0e0000
It makes me guess that is why it was added to the example I had.
Hmmm, I didn't remember DTC were throwing a warning.
What I want to avoid is writing in the documentation the phandle value. The
value has been chosen in random and we have no guarantee the phandle will not be
used by DTC in the future.
The solution I can think of is requesting the user to add the following snippet
in the partial DT.
interrupt-parent = &gic;
gic {
};
This will let DTC to define the phandle. Xen can then lookup for the patch /gic
and re-use the phandle for the guest GIC node.
What do you think?
Cheers,
--
Julien Grall
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