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

[Ingo Molnar]

* James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:

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