linux-kernel - Re: [PATCH V3 6/6] dt-bindings: xen: Clarify "reg" purpose

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Date:   Thu, 25 Nov 2021 14:21:36 +0200
From:   Oleksandr <olekstysh@...il.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     xen-devel@...ts.xenproject.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Julien Grall <julien@....org>
Subject: Re: [PATCH V3 6/6] dt-bindings: xen: Clarify "reg" purpose


On 25.11.21 03:09, Stefano Stabellini wrote:

Hi Stefano

> On Wed, 24 Nov 2021, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.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@...m.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@...nel.org>

Thanks!


-- 
Regards,

Oleksandr Tyshchenko