Re: [PATCH 0/3] GIC OF bindings

[Mitch Bradley]

On 9/20/2011 6:14 PM, Grant Likely wrote:
> On Tue, Sep 20, 2011 at 8:49 PM, David Miller<davem@xxxxxxxxxxxxx>  wrote:
> > From: Rob Herring<robherring2@xxxxxxxxx>
> > Date: Tue, 20 Sep 2011 15:24:01 -0500
> >
> > > Hopefully, this is the final or near final version of GIC binding support.
> > >
> > > Changes from the previous version:
> > > - SPIs and PPIs are numbered starting at 0. Now the gic has it's own irq
> > >    domain translate function instead of the simple domain one.
> > > - interrupt cell format has changed based on Grant's proposal.
> > > - Dropped "ARM: gic: allow irq_start to be 0". Instead, the first 16 irqs
> > >    are skipped and the domain irq_base adjusted accordingly.
> > > - Added a fix to of_irq_find_parent when the parent == child.
> > > - Renamed intc_desc.parent to intc_desc.interrupt_parent.
> > > - Implemented Grant's algorithm for walking the list of interrupt
> > >    controllers. Added a return value to interrupt init functions, so they
> > >    don't get added to the parent list on a init failure.
> > >
> > > The changes are significant enough that I did not include previous
> > > acked/reviewed/tested-by's.
> >
> > Just out of curiosity where does this "interrupt-parent" property
> > come from?
> >
> > On platforms I am familiar with, the parent path is walked to the root
> > and we stop at device nodes that have "interrupt-map" and
> > "interrupt-map-mask" properties.
> >
> > The map and mask are applied to the "reg" property of the device in
> > question to see which map entry matches, if a match is found the map
> > entry contains the translated interrupt.
> >
> > And this process continues over and over all the way to the root to get
> > the system interrupt that processor actually deals with.
> >
> > The mechanism shown here seems overly simplistic and not able to handle
> > the cases handled by existing OF property schemes in use for several
> > years on real systems.
>
> interrupt-parent has been implemented for years on powerpc.  I don't
> know if it was ever an Open Firmware thing, but it is in ePAPR [1],
> and ARM isn't doing anything novel in that regard.

interrupt-parent has been part of the interrupt mapping spec from the 
inception of same.

http://www.openfirmware.info/docs/rec.intmap.d09.pdf

> [1] section 2.4, page 30,
> https://www.power.org/resources/downloads/Power_ePAPR_APPROVED_v1.1.pdf
>
> It is true that is cannot handle all situations, but for those
> interrupt-map is still available.
>
> g.
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