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From: nicolas.pitre@linaro.org (Nicolas Pitre)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] ARM: proc-v7.S: Adjust stack address when XIP_KERNEL
Date: Tue, 16 Feb 2016 15:16:35 -0500 (EST)	[thread overview]
Message-ID: <alpine.LFD.2.20.1602161504400.13632@knanqh.ubzr> (raw)
In-Reply-To: <20160216173225.GE19428@n2100.arm.linux.org.uk>

On Tue, 16 Feb 2016, Russell King - ARM Linux wrote:

> > > index 0f92d57..1595fb2 100644
> > > --- a/arch/arm/mm/proc-v7.S
> > > +++ b/arch/arm/mm/proc-v7.S
> > > @@ -487,7 +487,7 @@ __errata_finish:
> > >  
> > >  	.align	2
> > >  __v7_setup_stack_ptr:
> > > -	.word	__v7_setup_stack - .
> > > +	.word	__v7_setup_stack - . + PHYS_OFFSET_FIXUP
> 
> I keep looking at this patch, and I really find that I detest this
> PHYS_OFFSET_FIXUP thing - it's really not obvious what's going on
> here.  It's taken a _long_ time to work this out, which _really_
> isn't good going forward.
> 
> Let's instead change things to make it much more obvious - see the
> patch below.
> 
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index ebdaaf7dd19f..593e5613184d 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -135,11 +135,18 @@
>  #define PLAT_PHYS_OFFSET	UL(CONFIG_PHYS_OFFSET)
>  
>  #ifdef CONFIG_XIP_KERNEL
> -#define PHYS_OFFSET_FIXUP \
> -	( XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR) - PAGE_OFFSET + \
> -	  PLAT_PHYS_OFFSET - CONFIG_XIP_PHYS_ADDR )
> +/*
> + * When referencing data in RAM from the XIP region in a relative manner
> + * with the MMU off, we need the relative offset between the two physical
> + * addresses.  The macro below achieves this, which is:
> + *    __pa(v_data) - __xip_pa(v_text)
> + */
> +#define PHYS_RELATIVE(v_data, v_text) \
> +	(((v_data) - PAGE_OFFSET + PLAT_PHYS_OFFSET) - \
> +	 ((v_text) - XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR) + \
> +          CONFIG_XIP_PHYS_ADDR))

Sure, this is less opaque.

>  #else
> -#define PHYS_OFFSET_FIXUP 0
> +#define PHYS_RELATIVE(v_data, v_text) (v_data) - (v_text)

You should probably surround the whole thing with parents in case this 
gets used in some other computations.


Nicolas

      parent reply	other threads:[~2016-02-16 20:16 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-29 22:11 [PATCH] ARM: proc-v7.S: Adjust stack address when XIP_KERNEL Chris Brandt
2016-01-31 23:20 ` Arnd Bergmann
2016-02-01 14:08   ` Chris Brandt
2016-02-01 14:08 ` [PATCH v2] " Chris Brandt
2016-02-01 21:15   ` Nicolas Pitre
2016-02-16 17:32     ` Russell King - ARM Linux
2016-02-16 18:53       ` Chris Brandt
2016-02-16 20:16       ` Nicolas Pitre [this message]

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