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

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Message-ID: <50572692.1090805@gmail.com>
Date:	Mon, 17 Sep 2012 08:33:06 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.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>,
	Dave Martin <dave.martin@...aro.org>
Subject: Re: [PATCH v4 06/24] docs: Xen ARM DT bindings

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@...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:
>>> +

State that they are part of top-level "hypervisor" node.

>>> +- 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.

> 
>>> +
>>> +
>>> +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.

Rob

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