linux-kernel - Re: Generic DT binding for IPIs

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Date:	Thu, 22 Oct 2015 11:44:16 +0100
From:	Qais Yousef <qais.yousef@...tec.com>
To:	<devicetree@...r.kernel.org>
CC:	<robh+dt@...nel.org>, <pawel.moll@....com>, <mark.rutland@....com>,
	<ijc+devicetree@...lion.org.uk>, <galak@...eaurora.org>,
	<tglx@...utronix.de>, <jason@...edaemon.net>,
	<marc.zyngier@....com>, <jiang.liu@...ux.intel.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: Generic DT binding for IPIs

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?

Thanks,
Qais

On 10/14/2015 11:18 AM, Qais Yousef wrote:
> Hi,
>
> This is an attempt to revive a discussion on the right list this time 
> with all the correct people hopefully on CC.
>
> While trying to upstream a driver, Thomas and Marc Zyngier pointed out 
> the need for a generic IPI support in the kernel to allow driver to 
> reserve and send ones. Hopefully my latest RFC patch will help to 
> clarify what's being done.
>
>     https://lkml.org/lkml/2015/10/13/227
>
> We need a generic DT binding support to accompany that to allow a 
> driver to reserve an IPI using this new mechanism.
>
> MarcZ had the following suggestion:
>
>     https://lkml.org/lkml/2015/8/24/628
>
> Which in summary is
>
>     mydevice@...00000 {
>         interrupt-source = <&intc INT_SPEC 2 &inttarg1 &inttarg1>;
>     };
>
>     inttarg1: mydevice@...00000 {
>         interrupt-sink = <&intc HWAFFINITY1>;
>     };
>
>     inttarg2: cpu@1 {
>         interrupt-sink = <&intc HWAFFINITY2>;
>     };
>
>
> interrupt-sink requests to reserve an IPI that it will receive at 
> HWAFFINITY cpumask. interrupt-source will not do any reservation. It 
> will simply connect an IPI reserved by interrupt-sink to the device 
> that will be responsible for generating that IPI. This description 
> should allow connecting any 2 devices.
> Correct me Marc if I got it wrong please.
>
> I suggested a simplification by assuming that IPIs will only be 
> between host OS and a coprocessor which would gives us this form which 
> I think is easier to deal with
>
>     coprocessor {
>              interrupt-source = <&intc INT_SPEC COP_HWAFFINITY>;
>              interrupt-sink = <&intc INT_SPEC CPU_HWAFFINITY>;
>     }
>
>
> interrupt-source here reserves an IPI to be sent from host OS to 
> coprocessor at COP_HWAFFINITY. interrupt-sink will reserve an IPI to 
> be received by host OS at CPU_HWAFFINITY. Less generic but I don't 
> know how important it is for host OS to setup IPIs between 2 external 
> coprocessors and whether it should really be doing that.
>
> What do the DT experts think? Any preference or a better suggestion?
>
> I tried to keep this short and simple, please let me know if you need 
> more info or if there's anything that needs more clarification.
>
> Thanks,
> Qais

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