linux-kernel - Re: [RFC PATCH] ARM: Add imprecise abort enable/disable macro

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Message-ID: <20140210135659.GU26684@n2100.arm.linux.org.uk>
Date:	Mon, 10 Feb 2014 13:56:59 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Will Deacon <will.deacon@....com>
Cc:	Fabrice Gasnier <fabrice.gasnier@...com>,
	"u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
	Jonathan Austin <Jonathan.Austin@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"nico@...aro.org" <nico@...aro.org>,
	"sboyd@...eaurora.org" <sboyd@...eaurora.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"ben.dooks@...ethink.co.uk" <ben.dooks@...ethink.co.uk>,
	"vgupta@...opsys.com" <vgupta@...opsys.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"maxime.coquelin@...com" <maxime.coquelin@...com>
Subject: Re: [RFC PATCH] ARM: Add imprecise abort enable/disable macro

On Mon, Feb 10, 2014 at 11:17:10AM +0000, Will Deacon wrote:
> On Mon, Feb 10, 2014 at 08:50:16AM +0000, Fabrice Gasnier wrote:
> > On 02/07/2014 06:09 PM, Will Deacon wrote:
> > > On Fri, Feb 07, 2014 at 04:19:15PM +0000, Fabrice GASNIER wrote:
> > >> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> > >> index 4636d56..ef15709 100644
> > >> --- a/arch/arm/kernel/traps.c
> > >> +++ b/arch/arm/kernel/traps.c
> > >> @@ -900,6 +900,10 @@ void __init early_trap_init(void *vectors_base)
> > >>   
> > >>   	flush_icache_range(vectors, vectors + PAGE_SIZE * 2);
> > >>   	modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
> > >> +
> > >> +	/* Enable imprecise aborts */
> > >> +	local_abt_enable();
> > > Surely we want to enable this as early as possible? Now, putting this into
> > > head.S is ugly, as it duplicating it across all the proc*.S files, so why
> > > not setup_arch?
> > Sorry, I'm not sure to understand your last comment.
> > At least, I need it enabled before probing drivers (PCIe bus)
> > I've added imprecise abort enable code in traps.c, following Russel 
> > King's advice, please see:
> > http://archive.arm.linux.org.uk/lurker/message/20140131.170827.d752a1cc.en.html
> > As abort bit is local to a cpu, i've also added it in smp.c, but this 
> > may not be the right place ?
> > 
> > Please elaborate,
> 
> I was just suggesting that we move your local_abt_enable() call to
> setup_arch, since that's called before early_trap_init on the primary CPU.

Why would we want to enable aborts before we've setup the vectors page
to handle an abort?  That's akin to enabling interrupts and hoping there
isn't one pending...

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