[PATCH 1/2] powerpc: document the MPIC device tree binding
meador_inge at mentor.com
Thu Jan 20 07:24:57 EST 2011
On 01/18/2011 02:21 PM, Yoder Stuart-B08248 wrote:
>> Documentation/powerpc/dts-bindings/mpic.txt | 78
> This is really the binding for an open-pic interrupt controller
> and I think the name should reflect that-- open-pic.txt.
>> +This binding specifies what properties and child nodes must be
>> +available on the device tree representation of the "MPIC" interrupt
>> +controller. This binding is based on the binding defined for Open PIC
>> +in  and is a superset of that binding.
> I think it would be better to base this on the ePAPR binding which
> was based on the original chrp binding. Properties like "name"
> and "device_type" are deprecated not being used in flat device trees.
> The proposed new properties really should go back into the ePAPR.
I read portions of ePAPR while writing this binding and considered that.
My only worry was that ePAPR is focused on embedded systems and this
binding will have to cover non-embedded systems that exist in the
kernel. However, perhaps that is not a legitimate concern?
>> +** Required properties:
>> + NOTE: Many of these descriptions were paraphrased from  to aid
>> + readability.
>> + - name : Specifies the name of the MPIC.
> Drop this. No DTS files use it.
>> + - device_type : Specifies the device type of this MPIC. The value
>> + of this
>> + property shall be "open-pic".
> device_type is deprecated, since this is not real open-firmware. In
> practice the kernel is matching on device_type, but we want to move
> away from that to match on "compatible", just hasn't been implemented
I will drop this property with the expectation that the kernel will be
fixed. From a quick grep of '.../arch/powerpc' it looks like most uses
are of the form:
np = of_find_node_by_type(NULL, "open-pic");
if (np == NULL)
In most of these cases I suppose the 'of_find_node_by_type' calls could
just be replaced with calls to 'of_find_compatible_node(NULL, "open-pic")'.
>> + - reg : Specifies the base physical address(s) and size(s) of this
>> + MPIC's
>> + addressable register space.
>> + - compatible : Specifies the compatibility list for the MPIC. The
>> + property
>> + value shall include "chrp,open-pic".
> In the ePAPR we modified this to just "open-pic", because this has
> nothing to do with chrp anymore. I think just "open-pic" is
> what we want.
OK, but as a migration path we should allow the kernel to accept both
(Scott mentioned this in another reply), but "open-pic" is the
documented correct way.
>> + - interrupt-controller : The presence of this property identifies
>> + the node
>> + as a MPIC. No property value should be
>> + - #address-cells : Specifies the number of cells needed to encode an
>> + address. The value of this property shall always
>> + be 0
>> + so that 'interrupt-map' nodes do not have to
>> + specify a
>> + parent unit address.
>> + - #interrupt-cells : Specifies the number of cells needed to encode
>> + an
>> + interrupt source.
> Should be 2, correct?
>> +** Optional properties:
>> + - no-reset : The presence of this property indicates that the MPIC
>> + should not be reset during runtime initialization.
>> + - protected-sources : Specifies a list of interrupt sources that are
>> + not
>> + available for use and whose corresponding
>> + vectors
>> + should not be initialized. A typical use case
>> + for
>> + this property is in AMP systems where multiple
>> + independent operating systems need to share
>> + the MPIC
>> + without clobbering each other.
> I do think you need to include the definition of interrupt
> specifiers here. Feel free to cut/paste text from my
> Freescale mpic binding.
OK, I will look into that. Thanks.
Meador Inge | meador_inge AT mentor.com
Mentor Embedded | http://www.mentor.com/embedded-software
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