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

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

[James Bottomley]

On Tue, 2009-02-17 at 21:12 +0000, H. Peter Anvin wrote:
> Author:     H. Peter Anvin <hpa@linux.intel.com>
> AuthorDate: Tue, 17 Feb 2009 13:01:51 -0800
> Commit:     H. Peter Anvin <hpa@linux.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@linux.intel.com>
> Cc: James Bottomley <James.Bottomley@hansenpartnership.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

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

[H. Peter Anvin]

James Bottomley wrote:
>> +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.
> 

Because a volatile is permitted.  virt_to_phys() takes a volatile 
pointer for that reason.

	-hpa

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

[Ingo Molnar]

* James Bottomley <James.Bottomley@HansenPartnership.com> wrote:

> On Tue, 2009-02-17 at 21:12 +0000, H. Peter Anvin wrote:
> > Author:     H. Peter Anvin <hpa@linux.intel.com>
> > AuthorDate: Tue, 17 Feb 2009 13:01:51 -0800
> > Commit:     H. Peter Anvin <hpa@linux.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@linux.intel.com>
> > Cc: James Bottomley <James.Bottomley@hansenpartnership.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.

That is because the volatile keyword here broadens the permitted 
_input_ type.

	Ingo