RE: pgprot_writecombine & shub 1.x

Luck, Tony
2005-01-19T22:00:42Z

>On Wednesday, January 19, 2005 10:04 am, David Mosberger wrote:
>> Adding new routines for supporting this sounds reasonable,
>but I think
>> it needs to be added to linux/efi.h, since EFI isn't ia64-specific.
>
>Something like this then? Works for my test cases.
>
>Add a new EFI memory map checking function called
>efi_range_is_wc for checking
>if address ranges can be mapped with the WC (write coalescing)
>attribute.
>Useful for fbmem, userspace PCI mapping, and other places where write
>combining might be beneficial but unavailable.

+ for (i = 0; i < len; i++) {
+ unsigned long paddr = __pa(start + i);
+ if (!(efi_mem_attributes(paddr) & EFI_MEMORY_WC))
+ return 0;
+ }

More EFI ignorance on my part ... do you really have to check
each *byte* of the address range, or is there some larger unit
that you could step by? It doesn't seem rational that this
attribute could change for anything less than cache line size.

-Tony