[RFC PATCH] powerpc: add ioremap_wt

[Gabriel Paubert]

On Mon, Feb 03, 2014 at 08:16:49AM +0100, Michael Moese wrote:
> Allow for IO memory to be mapped cacheable for performing
> PCI read bursts.
> 
> Signed-off-by: Michael Moese <michael.moese at men.de>
> ---
>  arch/powerpc/include/asm/io.h | 3 +++
>  arch/powerpc/mm/pgtable_32.c  | 8 ++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/io.h b/arch/powerpc/include/asm/io.h
> index 45698d5..9591fff 100644
> --- a/arch/powerpc/include/asm/io.h
> +++ b/arch/powerpc/include/asm/io.h
> @@ -631,6 +631,8 @@ static inline void iosync(void)
>   *
>   * * ioremap_wc enables write combining
>   *
> + * * ioremap_wc enables write thru

Typo: _wc -> _wt

Looks fine in principle, but there is a significant difference with wc
on x86, where read accesses always go to the bus (no read caching).

	Gabriel

> + *
>   * * iounmap undoes such a mapping and can be hooked
>   *
>   * * __ioremap_at (and the pending __iounmap_at) are low level functions to
> @@ -652,6 +654,7 @@ extern void __iomem *ioremap(phys_addr_t address, unsigned long size);
>  extern void __iomem *ioremap_prot(phys_addr_t address, unsigned long size,
>  				  unsigned long flags);
>  extern void __iomem *ioremap_wc(phys_addr_t address, unsigned long size);
> +extern void __iomem *ioremap_wt(phys_addr_t address, unsigned long size);
>  #define ioremap_nocache(addr, size)	ioremap((addr), (size))
>  
>  extern void iounmap(volatile void __iomem *addr);
> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> index 51f8795..9ab0a54 100644
> --- a/arch/powerpc/mm/pgtable_32.c
> +++ b/arch/powerpc/mm/pgtable_32.c
> @@ -141,6 +141,14 @@ ioremap_wc(phys_addr_t addr, unsigned long size)
>  EXPORT_SYMBOL(ioremap_wc);
>  
>  void __iomem *
> +ioremap_wt(phys_addr_t addr, unsigned long size)
> +{
> +	return __ioremap_caller(addr, size, _PAGE_WRITETHRU,
> +				__builtin_return_address(0));
> +}
> +EXPORT_SYMBOL(ioremap_wt);
> +
> +void __iomem *
>  ioremap_prot(phys_addr_t addr, unsigned long size, unsigned long flags)
>  {
>  	/* writeable implies dirty for kernel addresses */
> -- 
> 1.8.5.3
> 
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