linux-kernel - Re: [tip:x86/mm] x86/mm/mtrr: Clean up mtrr_type

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Message-ID: <20150801163311.GA15356@nazgul.tnic>
Date:	Sat, 1 Aug 2015 18:33:11 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	Toshi Kani <toshi.kani@...com>,
	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	hpa@...or.com, dvlasenk@...hat.com, bp@...e.de,
	akpm@...ux-foundation.org, brgerst@...il.com, tglx@...utronix.de,
	linux-mm@...ck.org, luto@...capital.net,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86/mm/mtrr: Clean up mtrr_type_lookup()

On Sat, Aug 01, 2015 at 04:28:20PM +0200, Luis R. Rodriguez wrote:
> I need to update this documentation to remove set_memory_wc() there as we've
> learned with the MTRR --> PAT conversion that set_memory_wc() cannot be used on
> IO memory, it can only be used for RAM. I am not sure if I would call it being
> broken that you cannot use set_memory_*() for IO memory that may have been by
> design.

Well, it doesn't really make sense to write-combine IO memory, does it?
My simplistic impression is that an IO range behind which there's a
device, cannot stomach any caching of IO as all commands/data accesses
need to happen as they get issued...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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