linux-kernel - Re: [PATCH v4 06/24] docs: Xen ARM DT bindings

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Date:	Fri, 14 Sep 2012 15:26:34 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"Tim (Xen.org)" <tim@....org>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	David Vrabel <david.vrabel@...rix.com>,
	Rob Herring <robherring2@...il.com>,
	Dave Martin <dave.martin@...aro.org>
Subject: Re: [PATCH v4 06/24] docs: Xen ARM DT bindings

On Fri, 14 Sep 2012, Konrad Rzeszutek Wilk wrote:
> On Fri, Sep 14, 2012 at 12:13:08PM +0100, Stefano Stabellini wrote:
> > Add a doc to describe the Xen ARM device tree bindings
> > 
> > 
> > Changes in v4:
> > 
> > - "xen,xen" should be last as it is less specific;
> > - update reg property using 2 address-cells and 2 size-cells.
> > 
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > CC: devicetree-discuss@...ts.ozlabs.org
> > CC: David Vrabel <david.vrabel@...rix.com>
> > CC: Rob Herring <robherring2@...il.com>
> > CC: Dave Martin <dave.martin@...aro.org>
> > ---
> >  Documentation/devicetree/bindings/arm/xen.txt |   22 ++++++++++++++++++++++
> >  1 files changed, 22 insertions(+), 0 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/arm/xen.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/arm/xen.txt b/Documentation/devicetree/bindings/arm/xen.txt
> > new file mode 100644
> > index 0000000..1f8f7d4
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/arm/xen.txt
> > @@ -0,0 +1,22 @@
> > +* Xen hypervisor device tree bindings
> > +
> > +Xen ARM virtual platforms shall have the following properties:
> > +
> > +- compatible:
> > +	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. 
> > +
> > +- interrupts: the interrupt used by Xen to inject event notifications.
> 
> Its singular here.. but in the example its plurar. What if you use
> multiple of the same number ("16 0xf")?

The "interrupts" property in the example below is a standard property to
describe interrupts. We just happen to declare only one interrupt.

>From the device tree point of view it would be possible to declare more
than one interrupt here, but Xen only supports one really.

Regarding the three cells used in the example (<1 15 0xf08>), they have
a specific meaning in the GIC context:

"""
  The 1st cell is the interrupt type; 0 for SPI interrupts, 1 for PPI
  interrupts.

  The 2nd cell contains the interrupt number for the interrupt type.
  SPI interrupts are in the range [0-987].  PPI interrupts are in the
  range [0-15].

  The 3rd cell is the flags, encoded as follows:
	bits[3:0] trigger type and level flags.
		1 = low-to-high edge triggered
		2 = high-to-low edge triggered
		4 = active high level-sensitive
		8 = active low level-sensitive
	bits[15:8] PPI interrupt cpu mask.  Each bit corresponds to each of
	the 8 possible cpus attached to the GIC.  A bit set to '1' indicated
	the interrupt is wired to that CPU.  Only valid for PPI interrupts.
"""

So <1 15 0xf08> means the last PPI.



> > +
> > +
> > +Example:
> > +
> > +hypervisor {
> > +	compatible = "xen,xen-4.3", "xen,xen";
> > +	reg = <0 0xb0000000 0 0x20000>;
> 
> So two grant tables?
> 
> Hm, physical address is zero, and the size is 0xbignumber?
> Or is the '0' denotating a seperator of arguments, so it is
> 0xb000.. for physical address and 0x20000 for size?

from http://devicetree.org/Device_Tree_Usage:

"Each addressable device gets a reg which is a list of tuples in the
form reg = <address1 length1 [address2 length2] [address3 length3] ...
Each tuple represents an address range used by the device. Each address
value is a list of one or more 32 bit integers called cells. Similarly,
the length value can either be a list of cells, or empty."

In this case the address is: [0 0xb0000000], that means
0x00000000b0000000, and the length is [0 0x20000], that means
0x0000000000020000.
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