[RFC][PATCH] [POWERPC] Allow caching of kmap_atomic page

[Benjamin Herrenschmidt]

On Fri, 2007-11-30 at 03:14 -0600, Kumar Gala wrote:
> Skip updating the kmap_pte and flushing the TLB if the pte we
> are about to write is the same as the one we wrote last time we
> called kmap_atomic for this km_type.
> 
> Also expose the flags to allow a caller to specify their own
> flags for things like non-cacheable IO memory.
> 
> ---
> 
> This is the starts of some work Ben and I were discussion to allow us to
> use kmap_atomic to access a page size region of PCI CFG space when its
> provided as direct MMIO.
> 
> We also intend to provide a means to preload the TLB for SW managed TLB
> machines.

We probably need to move that outside of highmem though...

Cheers,
Ben.

> - k
> 
>  include/asm-powerpc/highmem.h |   16 +++++++++++++---
>  1 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/include/asm-powerpc/highmem.h b/include/asm-powerpc/highmem.h
> index f7b21ee..a50bb00 100644
> --- a/include/asm-powerpc/highmem.h
> +++ b/include/asm-powerpc/highmem.h
> @@ -73,10 +73,12 @@ static inline void kunmap(struct page *page)
>   * be used in IRQ contexts, so in some (very limited) cases we need
>   * it.
>   */
> -static inline void *kmap_atomic(struct page *page, enum km_type type)
> +static inline void *__kmap_atomic(struct page *page,
> +				  enum km_type type, unsigned long flags)
>  {
>  	unsigned int idx;
>  	unsigned long vaddr;
> +	pte_t pte;
> 
>  	/* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
>  	pagefault_disable();
> @@ -88,12 +90,20 @@ static inline void *kmap_atomic(struct page *page, enum km_type type)
>  #ifdef HIGHMEM_DEBUG
>  	BUG_ON(!pte_none(*(kmap_pte+idx)));
>  #endif
> -	set_pte_at(&init_mm, vaddr, kmap_pte+idx, mk_pte(page, kmap_prot));
> -	flush_tlb_page(NULL, vaddr);
> +	pte = mk_pte(page, flags);
> +	if (!pte_same(kmap_pte[idx], pte)) {
> +		set_pte_at(&init_mm, vaddr, kmap_pte+idx, pte);
> +		flush_tlb_page(NULL, vaddr);
> +	}
> 
>  	return (void*) vaddr;
>  }
> 
> +static inline void *kmap_atomic(struct page *page, enum km_type type)
> +{
> +	return __kmap_atomic(page, type, kmap_prot);
> +}
> +
>  static inline void kunmap_atomic(void *kvaddr, enum km_type type)
>  {
>  #ifdef HIGHMEM_DEBUG