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

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Message-ID: <alpine.DEB.2.02.1304251104090.4180@kaball.uk.xensource.com>
Date:	Thu, 25 Apr 2013 11:12:54 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Will Deacon <will.deacon@....com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"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>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"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 Thu, 25 Apr 2013, Will Deacon wrote:
> > +/*
> > + * cpu_suspend   Suspend the execution on a CPU
> > + * @state        we don't currently describe affinity levels, so just pass 0.
> > + * @entry_point  the first instruction to be executed on return
> > + * returns 0  success, < 0 on failure
> > + *
> > + * cpu_off       Power down a CPU
> > + * @state        we don't currently describe affinity levels, so just pass 0.
> > + * no return on successful call
> > + *
> > + * cpu_on        Power up a CPU
> > + * @cpuid        cpuid of target CPU, as from MPIDR
> > + * @entry_point  the first instruction to be executed on return
> > + * returns 0  success, < 0 on failure
> > + *
> > + * migrate       Migrate the context to a different CPU
> > + * @cpuid        cpuid of target CPU, as from MPIDR
> > + * returns 0  success, < 0 on failure
> > + *
> > + */
> 
> Can you move these comments into psci-smp.c please? They're really specific
> to the implementation there, and if we put them in a header we're lying to
> ourselves about the parameters actually described by the PSCI specification.

You have a good point about the PSCI spec.

However from the Linux POV these comments should regard the functions
exported by psci_operations, not the firmware interface, this is why I
think it makes sense to keep them in psci.h.
What we are saying is for example that psci_operations.cpu_on returns 0
on success and < 0 on failure, and it takes a cpuid and an entry point
as parameters. We are not saying anything about the firmware interface.

Maybe I should add at the top:

"psci_operations functions and parameters, might different from the
firmware interface:"
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