linux-kernel - Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines

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Message-ID: <20100511215359.GF7396@core.coreip.homeip.net>
Date:	Tue, 11 May 2010 14:53:59 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Johannes Weiner <jw@...ix.com>
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Matt Mackall <mpm@...enic.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oskar Schirmer <os@...ix.com>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Daniel Glöckner <dg@...ix.com>,
	Oliver Schneidewind <osw@...ix.com>,
	Nick Piggin <npiggin@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines

On Tue, May 11, 2010 at 11:48:36PM +0200, Johannes Weiner wrote:
> On Tue, May 11, 2010 at 04:54:41PM -0400, Mike Frysinger wrote:
> > does the phrase "DMA safe buffer" imply cache alignment ?
> 
> I guess that depends on the architectural requirements.  On x86,
> apparently, not so much.  On ARM, probably yes, as it's the
> requirement to properly maintain coherency.

It looks liek ARM (and a few others) do this:

[dtor@...mer work]$ grep -r ARCH_KMALLOC_MINALIGN arch/
arch/sh/include/asm/page.h:#define ARCH_KMALLOC_MINALIGN        L1_CACHE_BYTES
arch/frv/include/asm/mem-layout.h:#define       ARCH_KMALLOC_MINALIGN           8
arch/powerpc/include/asm/page_32.h:#define ARCH_KMALLOC_MINALIGN        L1_CACHE_BYTES
arch/arm/include/asm/cache.h:#define ARCH_KMALLOC_MINALIGN      L1_CACHE_BYTES
arch/microblaze/include/asm/page.h:#define ARCH_KMALLOC_MINALIGN        L1_CACHE_BYTES
arch/mips/include/asm/mach-tx49xx/kmalloc.h: * All happy, no need to define ARCH_KMALLOC_MINALIGN
arch/mips/include/asm/mach-ip27/kmalloc.h: * All happy, no need to define ARCH_KMALLOC_MINALIGN
arch/mips/include/asm/mach-ip32/kmalloc.h:#define ARCH_KMALLOC_MINALIGN 32
arch/mips/include/asm/mach-ip32/kmalloc.h:#define ARCH_KMALLOC_MINALIGN 128
arch/mips/include/asm/mach-generic/kmalloc.h:#define ARCH_KMALLOC_MINALIGN      128
arch/avr32/include/asm/cache.h:#define ARCH_KMALLOC_MINALIGN    L1_CACHE_BYTES

-- 
Dmitry
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