linux-kernel - Re: [PATCH 1/2] ARCv2: Enable unaligned access in early ASM code

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Message-ID: <1548782756.29008.20.camel@synopsys.com>
Date:   Tue, 29 Jan 2019 17:25:57 +0000
From:   Eugeniy Paltsev <eugeniy.paltsev@...opsys.com>
To:     "Eugeniy.Paltsev@...opsys.com" <eugeniy.paltsev@...opsys.com>,
        "Vineet Gupta" <vineet.gupta1@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexey.brodkin@...opsys.com" <alexey.brodkin@...opsys.com>
Subject: Re: [PATCH 1/2] ARCv2: Enable unaligned access in early ASM code

On Tue, 2019-01-29 at 09:21 -0800, Vineet Gupta wrote:
> On 1/16/19 3:29 AM, Eugeniy Paltsev wrote:
> > Even though we do enable AD bit in arc_init_IRQ() we need to do
> > it in early ASM code otherwise we may face unaligned data until
> > we reach arc_init_IRQ() because GCC starting from v8.1.0 actively
> > generates unaligned data as it assumes that:
> >  * ARCv2 always has support of unaliged data
> >  * This support is turned on in runtime
> > 
> > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
> > ---
> >  arch/arc/kernel/head.S | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
> > index 8b90d25a15cc..d5b7a572365a 100644
> > --- a/arch/arc/kernel/head.S
> > +++ b/arch/arc/kernel/head.S
> > @@ -17,6 +17,9 @@
> >  #include <asm/entry.h>
> >  #include <asm/arcregs.h>
> >  #include <asm/cache.h>
> > +#ifdef CONFIG_ISA_ARCV2
> > +#include <asm/irqflags-arcv2.h>
> > +#endif
> 
> I presume there is no specific reason to include this conditionally.
> irqflags.h already includes the right version.

Agree.
I've just forgotten about common irqflags.h

Will fix in V2.

> >  
> >  .macro CPU_EARLY_SETUP
> >  
> > @@ -47,6 +50,13 @@
> >  	sr	r5, [ARC_REG_DC_CTRL]
> >  
> >  1:
> > +
> > +#ifdef CONFIG_ISA_ARCV2
> > +	; Enable handling of unaligned access in the CPU as by default
> > +	; this HW feature is disabled while GCC starting from 8.1.0
> > +	; unconditionally uses it for ARC HS cores.
> > +	flag    1 << STATUS_AD_BIT
> > +#endif
> >  .endm
> >  
> >  	.section .init.text, "ax",@progbits
> > 
> 
> 
-- 
 Eugeniy Paltsev