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SubjectRe: [PATCH V3 6/6] dt-bindings: xen: Clarify "reg" purpose
On Wed, 24 Nov 2021, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>
> Xen on Arm has gained new support recently to calculate and report
> extended regions (unused address space) safe to use for external
> mappings. These regions are reported via "reg" property under
> "hypervisor" node in the guest device-tree. As region 0 is reserved
> for grant table space (always present), the indexes for extended
> regions are 1...N.
>
> No device-tree bindings update is needed (except clarifying the text)
> as guest infers the presence of extended regions from the number
> of regions in "reg" property.
>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> ---
> According to the recent update to Xen's guest.txt:
> https://xenbits.xen.org/gitweb/?p=xen.git;a=blob_plain;f=docs/misc/arm/device-tree/guest.txt;hb=refs/heads/master
>
> Changes V2 -> V3:
> - new patch
> ---
> Documentation/devicetree/bindings/arm/xen.txt | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/arm/xen.txt b/Documentation/devicetree/bindings/arm/xen.txt
> index db5c56d..156fe10b 100644
> --- a/Documentation/devicetree/bindings/arm/xen.txt
> +++ b/Documentation/devicetree/bindings/arm/xen.txt
> @@ -7,10 +7,14 @@ the following properties:
> compatible = "xen,xen-<version>", "xen,xen";
> where <version> is the version of the Xen ABI of the platform.
>
> -- reg: specifies the base physical address and size of a region in
> - memory where the grant table should be mapped to, using an
> - HYPERVISOR_memory_op hypercall. The memory region is large enough to map
> - the whole grant table (it is larger or equal to gnttab_max_grant_frames()).
> +- reg: specifies the base physical address and size of the regions in memory
> + where the special resources should be mapped to, using an HYPERVISOR_memory_op
> + hypercall.
> + Region 0 is reserved for mapping grant table, it must be always present.
> + The memory region is large enough to map the whole grant table (it is larger
> + or equal to gnttab_max_grant_frames()).
> + Regions 1...N are extended regions (unused address space) for mapping foreign
> + GFNs and grants, they might be absent if there is nothing to expose.
> This property is unnecessary when booting Dom0 using ACPI.

I would remove the last sentence about ACPI as the initialization is not
done via the xen,xen device tree node in that case anyway.

With that change:

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

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