linux-kernel - Re: [PATCH 5/5] ARM: gic: add OF based initialization

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Date:	Mon, 19 Sep 2011 14:49:48 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Rob Herring <robherring2@...il.com>
Cc:	"Cousson, Benoit" <b-cousson@...com>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"marc.zyngier@....com" <marc.zyngier@....com>,
	"jamie@...ieiles.com" <jamie@...ieiles.com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH 5/5] ARM: gic: add OF based initialization

On Sun, Sep 18, 2011 at 04:23:40PM -0500, Rob Herring wrote:
> On 09/15/2011 11:43 AM, Rob Herring wrote:
> > I see 2 options (besides leaving it as is):
> > 
> > - Revert back to my previous binding where PPIs are a sub-node and a
> > different interrupt parent.
> > 
> > - Use the current binding, but allow SPIs to start at 0. We can still
> > distinguish PPIs and SPIs by the cpu mask cell. A cpu mask of 0 is a
> > SPI. If there was ever a reason to have a cpu mask for an SPI, you would
> > not be able to with this scheme.
> > 
> > Either way you will still have the above issue with the cell size changing.
> > 
> 
> I was headed down the path of implementing the 2nd option above, but had
> a dilemma. What would be the numbering base for PPIs in this case?
> Should it be 0 in the DT as proposed for SPIs or does it stay at 16?
> Numbering PPIs at 0 will just cause confusion as will numbering
> differently from SPIs. There is absolutely no mention of SPI0 or SPIx
> numbering in the GIC spec. All interrupt number references refer to the
> absolute interrupt ID, not a relative number based on the type.

Hi Rob,

See here[1] and [2] (figures 3.14 and 3.16).  In both cases, there is
clearly a reference to PPI numbering from 0-15 and SPI numbering from
0-987 (as inputs to the distributor block).

[1] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0416b/Bhacbfdb.html
[2] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0416b/Cihebcbg.html

g.
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