linux-kernel - Re: [tip:x86/headers] x86: truncate ISA addresses to unsigned int

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Message-Id: <1234905865.23466.11.camel@localhost.localdomain>
Date:	Tue, 17 Feb 2009 15:24:25 -0600
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de,
	hpa@...ux.intel.com, linux-kernel@...r.kernel.org
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/headers] x86: truncate ISA addresses to unsigned int

On Tue, 2009-02-17 at 21:12 +0000, H. Peter Anvin wrote:
> Author:     H. Peter Anvin <hpa@...ux.intel.com>
> AuthorDate: Tue, 17 Feb 2009 13:01:51 -0800
> Commit:     H. Peter Anvin <hpa@...ux.intel.com>
> CommitDate: Tue, 17 Feb 2009 13:01:51 -0800
> 
> x86: truncate ISA addresses to unsigned int
> 
> Impact: Cleanup; fix inappropriate macro use
> 
> ISA addresses on x86 are mapped 1:1 with the physical address space.
> Since the ISA address space is only 24 bits (32 for VLB or LPC) it
> will always fit in an unsigned int, and at least in the aha1542 driver
> using a wider type would cause an undesirable promotion.  Hence
> explicitly cast the ISA bus addresses to unsigned int.
> 
> Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
> Cc: James Bottomley <James.Bottomley@...senpartnership.com>
> 
> 
> ---
>  arch/x86/include/asm/io.h |   11 ++++++++---
>  1 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> index 4f8e820..683d0b4 100644
> --- a/arch/x86/include/asm/io.h
> +++ b/arch/x86/include/asm/io.h
> @@ -124,10 +124,15 @@ static inline void *phys_to_virt(phys_addr_t address)
>  
>  /*
>   * ISA I/O bus memory addresses are 1:1 with the physical address.
> + * However, we truncate the address to unsigned int to avoid undesirable
> + * promitions in legacy drivers.
>   */
> -#define isa_virt_to_bus (unsigned long)virt_to_phys
> -#define isa_page_to_bus page_to_phys
> -#define isa_bus_to_virt phys_to_virt
> +static inline unsigned int isa_virt_to_bus(volatile void *address)

The rest looks fine, but why is the address volatile?  The macro below
never actually dereferences it.

> +{
> +	return (unsigned int)virt_to_phys(address);
> +}
> +#define isa_page_to_bus(page)	((unsigned int)page_to_phys(page))
> +#define isa_bus_to_virt		phys_to_virt
>  
>  /*
>   * However PCI ones are not necessarily 1:1 and therefore these interfaces

James


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