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SubjectRe: [PATCH V4 6/6] dt-bindings: xen: Clarify "reg" purpose
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Hi Oleksandr,

> On 10 Dec 2021, at 11:36, Oleksandr Tyshchenko <olekstysh@gmail.com> 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>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

Cheers
Bertrand

> ---
> Changes V2 -> V3:
> - new patch
>
> Changes V3 -> V4:
> - add Stefano's R-b and Rob's A-b
> - remove sentence about ACPI for "reg" and "interrupts"
> properties
>
> Changes V4 -> V4.1
> - bring the mentioning of ACPI back which, as was pointed out by Julien,
> fits in the context:
> https://lore.kernel.org/xen-devel/9602b019-6c20-cdc7-23f3-9e4f8fd720f6@xen.org/T/#t
> so technically restore V3 state
> - remove Stefano's R-b and Rob's A-b as I am not 100% sure they are
> happy with that
> ---
> 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.
>
> - interrupts: the interrupt used by Xen to inject event notifications.
> --
> 2.7.4
>
>

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