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Date: Mon, 11 Sep 2006 23:48:33 -0600 From: ebiederm@...ssion.com (Eric W. Biederman) To: Alan Cox <alan@...rguk.ukuu.org.uk> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>, Linux Kernel list <linux-kernel@...r.kernel.org>, Jesse Barnes <jbarnes@...tuousgeek.org>, "David S. Miller" <davem@...emloft.net>, Jeff Garzik <jgarzik@...ox.com>, Paul Mackerras <paulus@...ba.org>, Linus Torvalds <torvalds@...l.org>, Andrew Morton <akpm@...l.org>, Segher Boessenkool <segher@...nel.crashing.org> Subject: Re: [RFC] MMIO accessors & barriers documentation Alan Cox <alan@...rguk.ukuu.org.uk> writes: >> > "Except where the underlying device is marked as cachable or >> > prefetchable" >> >> You aren't supposed to use MMIO accessors on cacheable memory, are you ? > > Why not. Providing it is in MMIO space, consider ROMs for example or > write path consider frame buffers. Frame buffers are rarely cachable as such, on x86 they are usually write-combining. Which means that the writes can be merged and possibly reordered while they are being written but they can't be cached. Most arches I believe have something that roughly corresponds to write combining. Ensuring we can still use this optimization to mmio space is moderately important. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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