linux-kernel - Re: [PATCH v6 1/4] arm: introduce psci_smp

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Date:	Mon, 22 Apr 2013 15:20:55 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
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>,
	"will.deacon@....com" <will.deacon@....com>,
	"arnd@...db.de" <arnd@...db.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"marc.zyngier@....com" <marc.zyngier@....com>
Subject: Re: [PATCH v6 1/4] arm: introduce psci_smp_ops

On Thu, Apr 18, 2013 at 12:35:57PM -0400, Nicolas Pitre wrote:
> On Thu, 18 Apr 2013, Stefano Stabellini wrote:
> 
> > On Thu, 18 Apr 2013, Russell King - ARM Linux wrote:
> > > On Fri, Apr 05, 2013 at 02:11:32PM +0100, Stefano Stabellini wrote:
> > > > +	psci_init();
> > > >  #ifdef CONFIG_SMP
> > > >  	if (is_smp()) {
> > > > -		smp_set_ops(mdesc->smp);
> > > > +		if (mdesc->smp)
> > > > +			smp_set_ops(mdesc->smp);
> > > > +		else if (psci_smp_available())
> > > > +			smp_set_ops(&psci_smp_ops);
> > > 
> > > So, I have a vague recollection that the ordering of the above got discussed
> > > but I can't find it amongst the 21k of messages so far this year.
> > > 
> > > The above looks weird to me.  Surely this should be:
> > > 
> > > 		if (psci_smp_available())
> > > 			smp_set_ops(&psci_smp_ops);
> > > 		else if (mdesc->smp)
> > > 			smp_set_ops(mdesc->ops);
> > > 
> > > This means that if PSCI is available, and provides a set of operations,
> > > we override whatever the platform has statically provided.
> > > 
> > > Remember, we're trying to move away from using "mdesc"s for platform
> > > stuff, relying on things like DT and such like.  We really should not
> > > be going for mdesc-overriding-newstuff but newstuff-overriding-mdesc.
> > 
> > That's correct, in fact if you look at the next patch you'll see that it
> > changes the order.
> > 
> > I introduced the mechanism first and changed the priority later - it
> > should help bisectability.
> > I can fold the two patches into one if you prefer.
> 
> Please let's keep the order as we discussed.  Otherwise this is just too 
> confusing (Russell's comment is a good example of that).

My comment is based on the code which I had read and quoted.  Things
had moved on from that point, but, because I had 2000 odd messages to
get through, there was no way to know at that point that there had been
further discussion.

This is why catching up is such a problem - not only the amount of time
it takes (I'm _still_ reading messages - I've only just read your reply
above, so I'm still back in Thursday's email...)

I don't think there's any confusion though - the order I suggested seems
to be the order which I recall later patches adopted.
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