FYI:
X86 and X86_64 kernels rely on MTRR to enable writecombining. X86 and X86_64 systems supports WriteCombining using the PAT bit in the PTE, but this is not yet supported by Linux kernels. ( There are no PAGE_PAT bit defiend and the PAT MSR power on value does not include support for the WC attribute.) After changing the PAT MSR to enable WC, I can do:
#define _PAGE_PAT 0x80 /* for AMD64 and X86 */ pgprot_val(vma->vm_page_prot) = pgprot_val(vma->vm_page_prot) |= _PAGE_PAT;
to set up a user space write combine map ( using mmmap())
and
__ioremap(ioaddr, size, _PAGE_PAT);
To set up a kernel space write combine map.
I can send the code to change the PAT MSR if anybody needs it - but I guess this is the wrong interest group (As this only works for x86/x86_64)
Best regards
Hugo
On Wed, 19 Jan 2005, David Mosberger wrote:
Date: Wed, 19 Jan 2005 14:20:21 -0800 From: David Mosberger <[EMAIL PROTECTED]> Reply-To: [EMAIL PROTECTED] To: Jesse Barnes <[EMAIL PROTECTED]> Cc: [EMAIL PROTECTED], Jim Hull <[EMAIL PROTECTED]>, [email protected], 'Tony Luck' <[EMAIL PROTECTED]> Subject: Re: pgprot_writecombine & shub 1.x
On Wed, 19 Jan 2005 14:16:28 -0800, Jesse Barnes <[EMAIL PROTECTED]> said:
Jesse> No, it still depends on pgprot_writecombined, which is ia64 Jesse> specific.
Not exactly ia64-specific, but yeah, I see x86 doesn't have it (I thought it did).
Jesse> x86 has its own way to set the wc bit and afaik doesn't have Jesse> the same aliasing issues that ia64 has.
In my opinion, an EFI-based system should respect the attribute-restrictions specified in the memory-map.
--david - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
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