From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tim Deegan <tim@xen.org>
Subject: Re: [PATCH 4/7] xen/arm: set the SMP bit in the ACTLR
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Date: Fri, 26 Oct 2012 09:56:15 +0100
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To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>
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At 13:04 +0100 on 25 Oct (1351170270), Ian Campbell wrote:
> On Thu, 2012-10-25 at 12:57 +0100, Stefano Stabellini wrote:
> > On Thu, 25 Oct 2012, Ian Campbell wrote:
> > > On Wed, 2012-10-24 at 16:03 +0100, Stefano Stabellini wrote:
> > > > From the Cortex A15 manual:
> > > > 
> > > > "Enables the processor to receive instruction cache, BTB, and TLB maintenance
> > > > operations from other processors"
> > > > 
> > > > ...
> > > > 
> > > > "You must set this bit before enabling the caches and MMU, or
> > > > performing any cache and TLB maintenance operations. The only time
> > > > you must clear this bit is during a processor power-down sequence"
> > > 
> > > Is it considered a bug that the firmware doesn't do this?
> > 
> > Why would it be? You can run fairly complicated pieces of software
> > without caches or MMU.
> 
> True, I guess I just considered that not setting the SMP bit on the
> second processor when the firmware starts it seemed a bit odd. If you
> aren't caches/MMU/etc them then setting the bit is pretty much a NOP (or
> maybe it isn't?).

Well, given that you're not allowed to clear it except at power-down, I
think it would be impolite of the firmware to set it if there's _any_
reason the OS might not want it set.

Tim.