Re: [Xen-devel] [PATCH 5/5] xen/arm: add dom0less device assignment info to docs

[Julien Grall <julien.grall@xxxxxxx>]

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"

> +
> +- 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.
> +
> +- 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.
> +
> +- path
> +
> +  A new string property named "path" holds the path in the host device
> +  tree to the corresponding device node.
This name is too generic. Please prepend "xen,"

> +
> +The following is a real-world example of a device tree fragment for the
> +network card on Xilinx MPSoC boards:
> +
> +/dts-v1/;
> +
> +/ {
> +    #address-cells = <0x2>;
> +    #size-cells = <0x1>;
> +
> +    passthrough {
> +        compatible = "simple-bus";
> +        ranges;
> +        #address-cells = <0x2>;
> +        #size-cells = <0x1>;
> +
> +        misc_clk {
> +            #clock-cells = <0x0>;
> +            clock-frequency = <0x7735940>;
> +            compatible = "fixed-clock";
> +            linux,phandle = <0x1>;
> +            phandle = <0x1>;
> +        };
> +
> +        ethernet@ff0e0000 {
> +            compatible = "cdns,zynqmp-gem";
> +            status = "okay";
> +            interrupt-parent = <0xfde8>;
> +            interrupts = <0x0 0x3f 0x4 0x0 0x3f 0x4>;
> +            reg = <0x0 0xff0e0000 0x1000>;
> +            clock-names = "pclk", "hclk", "tx_clk", "rx_clk";
> +            #address-cells = <0x1>;
> +            #size-cells = <0x0>;
> +            clocks = <0x1 0x1 0x1 0x1>;
> +            phy-mode = "rgmii-id";
> +            xlnx,ptp-enet-clock = <0x0>;
> +            local-mac-address = [00 0a 35 00 22 01];
> +            phy-handle = <0x2>;
> +            path = "/amba/ethernet@ff0e0000";
> +
> +            phy@c {
> +                reg = <0xc>;
> +                ti,rx-internal-delay = <0x8>;
> +                ti,tx-internal-delay = <0xa>;
> +                ti,fifo-depth = <0x1>;
> +                ti,rxctrl-strap-worka;
> +                linux,phandle = <0x2>;
> +                phandle = <0x2>;
> +            };
> +        };
> +    };
> +};
Cheers,

--
Julien Grall

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