Re: [Xen-devel] [PATCH v3 6/6] xen/arm: add dom0less device assignment info to docs

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

I figured out I may want to read the docs before looking at the code :).

On 09/08/2019 00:12, Stefano Stabellini wrote:
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
>
> ---
> Changes in v3:
> - add nr_spis
> - change description of interrupts and interrupt-parent
>
> Changes in v2:
> - device tree fragment loaded in cacheable memory
> - rename multiboot,dtb to multiboot,device-tree
> - rename "path" to "xen,path"
> - add a note about device memory mapping
> - introduce xen,reg
> - specify only the GIC is supported
> ---
>   docs/misc/arm/device-tree/booting.txt | 117 ++++++++++++++++++++++++++
>   1 file changed, 117 insertions(+)
>
> diff --git a/docs/misc/arm/device-tree/booting.txt 
> b/docs/misc/arm/device-tree/booting.txt
> index 317a9e962a..ec2f7ba605 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -148,6 +148,12 @@ with the following properties:
>   
>       An empty property to enable/disable a virtual pl011 for the guest to use.
>   
> +- nr_spis
> +    Optional. A 32-bit integer specifying the number of SPIs (shared
> +    perhiperal interrupts) to allocate for the domain. If nr_spis is
s/perhiperal/peripheral/. Also can you uppercase the first letter of each 
wording as you are spelling out an acronym?
> +    missing, the max number of SPIs supported by the physical GIC is
> +    used.
> +
>   - #address-cells and #size-cells
>   
>       Both #address-cells and #size-cells need to be specified because
> @@ -226,3 +232,114 @@ chosen {
>           };
>       };
>   };
> +
> +
> +Device Assignment
> +=================
Couldn't we just extend the file misc/arm/passthrough.txt? After all there 
should be no major difference between the two.
> +
> +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,device-tree"
Can we follow the convention for dom0? I.e you always have to pass 
"multiboot,module"? And probably suggest an order if the compatible 
"multiboot,device-tree" is not specified.
This would help to keep everything similar between dom0 and domU. Longer term, I 
would love to see Dom0 described exactly the same way as domU.
You would need to do the same update for multiboot,{kernel, ramdisk}.

> +
> +- reg
> +
> +    Specifies the physical address of the device tree binary fragment
> +    RAM and its length.
> +
> +As an example:
> +
> +        module@0xc000000 {
> +            compatible = "multiboot,device-tree", "multiboot,module";
> +            reg = <0x0 0xc000000 0xffffff>;
> +        };
> +
> +The DTB fragment is loaded in cacheable memory, at 0xc000000 in the
> +example above. It should follow the convention explained in
This is a bit confusing, how does the user know that 0xc0000000 is cachable 
memory? Also why you do mention it for device-tree and not kernel and initramfs?
> +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:
> +
> +- xen,reg
> +
> +  The xen,reg property is an array of:
> +
> +    <phys_addr size guest_addr>
> +
> +  They specify the physical address and size of the device memory
> +  ranges together with the corresponding guest address to map them to.
> +  The size of `phys_addr' and `guest_addr' is determined by
> +  #address_cells; the size of `size' is determined by #size_cells.
> +  The memory will be mapped as device memory in the guest
> +  (p2m_mmio_direct_dev).
> +
> +- xen,path
> +
> +  A new string property named "xen,path" holds the path in the host device
> +  tree to the corresponding device node.
> +
> +Please note that for GIC interrupts, the interrupts and interrupt-parent
> +device tree properties should not be present in the device tree
> +fragment, because they are automatically generated by Xen starting from
> +the corresponding information on the host device tree node for the
> +device. For GIC interrupts, only the interrupts property is currently
> +supported, not the newer interrupts-extended property.
Why so? There are a lot of Device-Tree that are switching to interrupts-extend 
for GIC interrupts....
Also, what about the property interrupt-map?

> +
> +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";
> +            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>;
> +            xen,path = "/amba/ethernet@ff0e0000";
> +            xen,reg = <0x0 0xff0e0000 0x1000 0x0 0xff0e0000>;
> +
> +            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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