linux-kernel - Re: Generic DT binding for IPIs

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Date:	Thu, 10 Dec 2015 11:49:41 +1100
From:	David Gibson <david@...son.dropbear.id.au>
To:	Rob Herring <robh+dt@...nel.org>
Cc:	Qais Yousef <qais.yousef@...tec.com>,
	"devicetree-spec@...r.kernel.org" <devicetree-spec@...r.kernel.org>,
	Jason Cooper <jason@...edaemon.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marc Zyngier <marc.zyngier@....com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lisa Parratt <Lisa.Parratt@...tec.com>
Subject: Re: Generic DT binding for IPIs

On Wed, Dec 09, 2015 at 10:50:35AM -0600, Rob Herring wrote:
> On Wed, Dec 9, 2015 at 9:27 AM, Qais Yousef <qais.yousef@...tec.com> wrote:
> > Hi,
> >
> > On 10/22/2015 12:55 PM, Jason Cooper wrote:
> >>
> >> On Thu, Oct 22, 2015 at 11:44:16AM +0100, Qais Yousef wrote:
> >>>
> >>> Is there anything more I can do to get more attention about this? I
> >>> think Marc's suggestion is more generic and future proof, if I send
> >>> RFC patches for that would this be better?
> >>
> >> Please do.
> >
> >
> > Unfortunately I haven't had a chance to get around writing the patches yet.
> > I came up with a different description though that I thought maybe worth
> > sharing
> > to see if there's any opinion about it before the actual work being done.
> 
> I've not given this too much thought, but here's my initial thoughts.
> 
> >
> > To summarise, the problem I am trying to solve is that we have a type of
> > coprocessors which share the interrupt controller with Linux, hence the IPI
> > mechanism this controller uses. I've been working with Thomas on
> > implementing
> > a generic API to allocate IPIs for coprocesors and a way for drivers to send
> > these IPIs [1].
> >
> > To complement this new API, we need a mechanism to describe this in
> > device tree so a driver that wants to allocate an IPI can have this done
> > automatically for it like we handle interrupts.
> >
> > What I have in mind is:
> >
> >      coproc {
> >              ipi-parent = <&gic>;
> >
> >              ipis = <CPU_VALUE IPI_SPEC>;
> >              ipi-names = "in";
> >      };
> >
> > This will allocate an IPI to go to cpu @CPU_VALUE passing @IPI_SPEC as
> > parameters to the controller. Which means we need a new ipi-cells to
> > define how many cells are in ipis property. Note the new ipi-parent too.
> 
> These are still interrupts, so I'd prefer to use or extend the
> interrupt binding if possible.

I agree.  It should be possible to just describe these as interrupts,
with the interrupt-parent being a special interrupt controller node to
represent these IPIs.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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