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

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
To: Rob Herring <robherring2@gmail.com>
Cc: Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	"arnd@arndb.de" <arnd@arndb.de>,
	"linux@arm.linux.org.uk" <linux@arm.linux.org.uk>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"linaro-dev@lists.linaro.org" <linaro-dev@lists.linaro.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"Tim (Xen.org)" <tim@xen.org>,
	Ian Campbell <Ian.Campbell@citrix.com>,
	"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"devicetree-discuss@lists.ozlabs.org" 
	<devicetree-discuss@lists.ozlabs.org>,
	David Vrabel <david.vrabel@citrix.com>,
	Dave Martin <dave.martin@linaro.org>
Subject: Re: [PATCH v4 06/24] docs: Xen ARM DT bindings
Date: Mon, 17 Sep 2012 15:12:11 +0100	[thread overview]
Message-ID: <alpine.DEB.2.02.1209171508470.29232@kaball.uk.xensource.com> (raw)
In-Reply-To: <50572692.1090805@gmail.com>

On Mon, 17 Sep 2012, Rob Herring wrote:
> On 09/14/2012 09:26 AM, Stefano Stabellini wrote:
> > 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@eu.citrix.com>
> >>> CC: devicetree-discuss@lists.ozlabs.org
> >>> CC: David Vrabel <david.vrabel@citrix.com>
> >>> CC: Rob Herring <robherring2@gmail.com>
> >>> CC: Dave Martin <dave.martin@linaro.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:
> >>> +
> 
> State that they are part of top-level "hypervisor" node.

OK

> >>> +- 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.
> 
> Since it is a PPI, it is handled differently than a normal interrupt.
> That is fine, but you should somehow state that a GIC node is also required.

Yes, good idea

> >>> +
> >>> +
> >>> +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.
> 
> But the size depends on #size-cells and #address-cells. I would expect
> those to be 1 for a 32-bit guest.

I was looking at the Versatile Express DTS (vexpress-v2p-ca15-tc1.dts)
that on Linux v3.6-rc5 has:

#address-cells = <2>;
#size-cells = <2>;

What should I use for the example in this doc?