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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 20 Jun 2017, Julien Grall wrote:
> 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.

I'll do, thanks


> > +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
> 

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