diff mbox series

[V4,6/6] dt-bindings: xen: Clarify "reg" purpose

Message ID 1639080336-26573-7-git-send-email-olekstysh@gmail.com (mailing list archive)
State Accepted
Commit 54bb4a91b281e1b21235a4bc175e1293e787c016
Headers show
Series xen: Add support of extended regions (safe ranges) on Arm | expand

Commit Message

Oleksandr Tyshchenko Dec. 9, 2021, 8:05 p.m. UTC 
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.

While at it, remove the following sentence:
"This property is unnecessary when booting Dom0 using ACPI."
for "reg" and "interrupts" properties as the initialization is not
done via device-tree "hypervisor" node in that case anyway.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
---
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
---
 Documentation/devicetree/bindings/arm/xen.txt | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

Comments

Julien Grall Dec. 10, 2021, 9:09 a.m. UTC | #1 
Hi Oleksandr,

On 09/12/2021 20:05, 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.
> 
> While at it, remove the following sentence:
> "This property is unnecessary when booting Dom0 using ACPI."
> for "reg" and "interrupts" properties as the initialization is not
> done via device-tree "hypervisor" node in that case anyway.
You sent a similar patch for Xen and have already commented there [1] . 
In short, the OS will be using the node to discover whether it is 
running on Xen for both ACPI and DT. The hypervisor node also contain 
the UEFI information for dom0.

Cheers,

[1] 
https://lore.kernel.org/xen-devel/9602b019-6c20-cdc7-23f3-9e4f8fd720f6@xen.org/T/#t
Oleksandr Tyshchenko Dec. 10, 2021, 9:33 a.m. UTC | #2 
On 10.12.21 11:09, Julien Grall wrote:
> Hi Oleksandr,


Hi Julien


>
> On 09/12/2021 20:05, 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.
>>
>> While at it, remove the following sentence:
>> "This property is unnecessary when booting Dom0 using ACPI."
>> for "reg" and "interrupts" properties as the initialization is not
>> done via device-tree "hypervisor" node in that case anyway.
> You sent a similar patch for Xen and have already commented there [1] 
> . In short, the OS will be using the node to discover whether it is 
> running on Xen for both ACPI and DT. The hypervisor node also contain 
> the UEFI information for dom0.

I agree with your comments. The sentence should remain in this case. 
Thank you for pointing this out.


>
>
> Cheers,
>
> [1] 
> https://lore.kernel.org/xen-devel/9602b019-6c20-cdc7-23f3-9e4f8fd720f6@xen.org/T/#t
>
diff mbox series

Patch

diff --git a/Documentation/devicetree/bindings/arm/xen.txt b/Documentation/devicetree/bindings/arm/xen.txt
index db5c56d..61d77ac 100644
--- a/Documentation/devicetree/bindings/arm/xen.txt
+++ b/Documentation/devicetree/bindings/arm/xen.txt
@@ -7,15 +7,17 @@  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()).
-  This property is unnecessary when booting Dom0 using ACPI.
+- 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.
 
 - interrupts: the interrupt used by Xen to inject event notifications.
   A GIC node is also required.
-  This property is unnecessary when booting Dom0 using ACPI.
 
 To support UEFI on Xen ARM virtual platforms, Xen populates the FDT "uefi" node
 under /hypervisor with following parameters: