Re: [Xen-devel] [PATCH] docs: improve ARM passthrough doc

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 06/16/2017 09:29 PM, Stefano Stabellini wrote:
> Add a warning: use passthrough with care.
>
> Add a pointer to the gic device tree bindings. Add an explanation on how
> to calculate irq numbers from device tree.
>
> Add a brief explanation of the reg property and a pointer to the xl docs
> for a description of the iomem property. Add a note that in the example
> we are using different memory addresses for guests and host.
>
> Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>
> diff --git a/docs/misc/arm/passthrough.txt b/docs/misc/arm/passthrough.txt
> index 082e9ab..7140a61 100644
> --- a/docs/misc/arm/passthrough.txt
> +++ b/docs/misc/arm/passthrough.txt
> @@ -12,7 +12,11 @@ property "xen,passthrough". The command to do it in U-Boot 
> is:
>   2) Create a partial device tree describing the device. The IRQ are mapped
>   1:1 to the guest (i.e VIRQ == IRQ). For MMIO, you will have to find a hole
>   in the guest memory layout (see xen/include/public/arch-arm.h, note that
> -the layout is not stable and can change between versions of Xen).
> +the layout is not stable and can change between versions of Xen). Please
> +be aware that passing a partial device tree to a VM is a powerful tool,
> +use it with care. In production, only allow assignment of devices which
> +have been previously tested and known to work correctly when given to
> +guests.
>   
>   /dts-v1/;
>   
> @@ -48,6 +52,8 @@ Note:
>           - #size-cells
>       * See http://www.devicetree.org/Device_Tree_Usage for more
>       information about device tree.
> +    * In this example, the device MMIO region is placed at a different
> +    address (0x10000000) compared to the host address (0xfff51000)
>   
>   3) Compile the partial guest device with dtc (Device Tree Compiler).
>   For our purpose, the compiled file will be called guest-midway.dtb and
> @@ -60,3 +66,16 @@ dtdev = [ "/soc/ethernet@fff51000" ]
>   irqs = [ 112, 113, 114 ]
>   iomem = [ "0xfff51,1@0x10000" ]
>   
> +Please refer to your platform docs for the MMIO ranges and interrupts.
> +
> +They can also be calculated from the original device tree (not
> +recommended). See [arm,gic.txt] in the Linux repository for a
[arm,gic.txt] documentation is only valid for GICv2. GICv3 has a 
different documentation, though the interrupt format is the same at the 
moment.
I think this should be clarified and explain that the interrupt format 
will depend on the virtual interrupt controller exposed to the guest.
> +description of the "interrupts" property format. For the GIC, the first
> +cell is interrupt type, and the second cell is the interrupt number.
> +Given that SPI numbers start from 32, in this example 80 + 32 = 112. > +
> +See man [xl.cfg] for the iomem format. The reg property is just a pair
> +of address, then size nunbers, each of them can occupy 1 or 2 cells.
s/nunbers/numbers/

> +
> +[arm,gic.txt]: 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/interrupt-controller/arm,gic.txt
> +[xl.cfg]: https://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html
Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel