linux-kernel - Re: [PATCH v3 13/17] ARM: Xen: Document UEFI support on Xen ARM virtual platforms

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Message-ID: <alpine.DEB.2.02.1601251604150.9687@kaball.uk.xensource.com>
Date:	Mon, 25 Jan 2016 16:06:10 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Shannon Zhao <zhaoshenglong@...wei.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<ard.biesheuvel@...aro.org>, <stefano.stabellini@...rix.com>,
	<david.vrabel@...rix.com>, <catalin.marinas@....com>,
	<will.deacon@....com>, <julien.grall@...rix.com>,
	<xen-devel@...ts.xen.org>, <devicetree@...r.kernel.org>,
	<linux-efi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<ian.campbell@...rix.com>, <shannon.zhao@...aro.org>,
	<peter.huangpeng@...wei.com>, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v3 13/17] ARM: Xen: Document UEFI support on Xen ARM
 virtual platforms

On Mon, 25 Jan 2016, Mark Rutland wrote:
> On Mon, Jan 25, 2016 at 03:50:52PM +0000, Stefano Stabellini wrote:
> > On Sat, 23 Jan 2016, Shannon Zhao wrote:
> > > From: Shannon Zhao <shannon.zhao@...aro.org>
> > > 
> > > Add a "uefi" node under /hypervisor node in FDT, then Linux kernel could
> > > scan this to get the UEFI information.
> > > 
> > > Signed-off-by: Shannon Zhao <shannon.zhao@...aro.org>
> > > Acked-by: Rob Herring <robh@...nel.org>
> > > ---
> > > CC: Rob Herring <robh@...nel.org>
> > > ---
> > >  Documentation/devicetree/bindings/arm/xen.txt | 34 +++++++++++++++++++++++++++
> > >  1 file changed, 34 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/arm/xen.txt b/Documentation/devicetree/bindings/arm/xen.txt
> > > index 0f7b9c2..aa69405 100644
> > > --- a/Documentation/devicetree/bindings/arm/xen.txt
> > > +++ b/Documentation/devicetree/bindings/arm/xen.txt
> > > @@ -15,6 +15,26 @@ the following properties:
> > >  - interrupts: the interrupt used by Xen to inject event notifications.
> > >    A GIC node is also required.
> > >  
> > > +To support UEFI on Xen ARM virtual platforms, Xen populates the FDT "uefi" node
> > > +under /hypervisor with following parameters:
> > > +
> > > +________________________________________________________________________________
> > > +Name                      | Size   | Description
> > > +================================================================================
> > > +xen,uefi-system-table     | 64-bit | Guest physical address of the UEFI System
> > > +			  |	   | Table.
> > > +--------------------------------------------------------------------------------
> > > +xen,uefi-mmap-start       | 64-bit | Guest physical address of the UEFI memory
> > > +			  |	   | map.
> > > +--------------------------------------------------------------------------------
> > > +xen,uefi-mmap-size        | 32-bit | Size in bytes of the UEFI memory map
> > > +                          |        | pointed to in previous entry.
> > > +--------------------------------------------------------------------------------
> > > +xen,uefi-mmap-desc-size   | 32-bit | Size in bytes of each entry in the UEFI
> > > +                          |        | memory map.
> > > +--------------------------------------------------------------------------------
> > > +xen,uefi-mmap-desc-ver    | 32-bit | Version of the mmap descriptor format.
> > > +--------------------------------------------------------------------------------
> > >  
> > >  Example (assuming #address-cells = <2> and #size-cells = <2>):
> > >  
> > > @@ -22,4 +42,18 @@ hypervisor {
> > >  	compatible = "xen,xen-4.3", "xen,xen";
> > >  	reg = <0 0xb0000000 0 0x20000>;
> > >  	interrupts = <1 15 0xf08>;
> > > +	uefi {
> > > +		xen,uefi-system-table = <0xXXXXXXXX>;
> > > +		xen,uefi-mmap-start = <0xXXXXXXXX>;
> > > +		xen,uefi-mmap-size = <0xXXXXXXXX>;
> > > +		xen,uefi-mmap-desc-size = <0xXXXXXXXX>;
> > > +		xen,uefi-mmap-desc-ver = <0xXXXXXXXX>;
> > > +        };
> > >  };
> > > +
> > > +The format and meaning of these "xen,uefi-*" parameters are similar to those in
> > > +Documentation/arm/uefi.txt which are used by normal UEFI. But to distinguish
> > > +from normal UEFI, for Xen ARM virtual platforms it needs to introduce a Xen
> > > +specific UEFI which requires Xen hypervisor to provide hypercalls for Dom0 to
> > > +make use of the runtime services. Therefore, it defines these parameters under
> > > +/hypervisor node.
> > 
> > Please replace the paragraph with the following which mentions
> > include/xen/interface/platform.h and improves the wording:
> > 
> > "The format and meaning of the "xen,uefi-*" parameters are similar to
> > those in Documentation/arm/uefi.txt, which are provided by the regular
> > UEFI stub. However they differ because they are provided by the Xen
> > hypervisor, together with a set of UEFI runtime services implemented via
> > hypercalls, see include/xen/interface/platform.h."
> 
> I would prefer if we didn't refer to Linux paths here, for the usual
> rationale of keeping bindings distinct from Linux implementation
> details.
> 
> Could we either drop the "see include/xen/interface/platform.h" part, or
> refer to some Xen documentation?

Sure, in fact the canonical headers are the ones in the Xen tree anyway.
We could use the following instead:

http://xenbits.xen.org/docs/unstable/hypercall/x86_64/include,public,platform.h.html