linux-kernel - Re: [PATCH v8 1/2] arm: introduce psci_smp

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Message-ID: <20130426161012.GH30858@mudshark.cambridge.arm.com>
Date:	Fri, 26 Apr 2013 17:10:12 +0100
From:	Will Deacon <will.deacon@....com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"olof@...om.net" <olof@...om.net>
Subject: Re: [PATCH v8 1/2] arm: introduce psci_smp_ops

On Fri, Apr 26, 2013 at 04:36:26PM +0100, Stefano Stabellini wrote:
> On Thu, 25 Apr 2013, Nicolas Pitre wrote:
> > On Thu, 25 Apr 2013, Will Deacon wrote:
> > > I disagree. You're explicitly stating that we pass the `cpuid of target CPU,
> > > as from MPIDR'. That's simply not true -- the firmware could choose any
> > > numbering scheme to identify the CPUs. For KVM and Xen, it *is* the mpidr,
> > > which is why psci-smp.c works at all, but that's where the comment belongs,
> > > not in this header file.
> > 
> > At some point, the _kernel_ API for interfacing with the firmware's PSCI 
> > will have to ensure uniformity somehow.  The PSCI interface code could 
> > translate the passed MPIDR into whatever the firmware decided to use for 
> > identifying CPUs if needed, keeping this issue localized.
> 
> That is what I had in mind when I said to keep the comment in psci.h
> before.
> We have to draw the line somewhere to expose a uniform internal kernel
> API. However it is a bit difficult to do now given that we have only one
> user of the API.

I see psci.h as representing the firmware interface, and psci-smp.c or
whatever sits on top as exposing the kernel `API'.

> I don't feel to strongly about this, please let me know what is the
> final decision and I'll update the code accordingly. I remind you that
> the merge window is approaching :-)

I'd still like the comment to be in psci-smp.c, or a header separate from
the firmware bits.

Will
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