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

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Date:	Mon, 10 Feb 2014 14:12:07 +0000
From:	Will Deacon <will.deacon@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
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 01:56:59PM +0000, Russell King - ARM Linux wrote:
> 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...

I figured we'd want to fall over as quickly as possible if the bootloader
had left a pending exception for us, but you're right in that it's not very
helpful if we can't print out a diagnostic.

Fabrice, please ignore my suggestion and keep the unmasking where it is.

Will
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