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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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