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    SubjectRe: [PATCH V3 6/6] dt-bindings: xen: Clarify "reg" purpose
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    On 25.11.21 03:09, Stefano Stabellini wrote:

    Hi Stefano

    > 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.

    Agree, will do. I assume, the similar sentence for the "interrupts"
    property down the text wants removing as well.


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

    Thanks!


    --
    Regards,

    Oleksandr Tyshchenko

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