linux-kernel - Re: [PATCH 2/2] scsi: Use new __dma_buffer to align sense buffer in scsi

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Message-ID: <adak5n8x9x0.fsf@cisco.com>
Date:	Fri, 21 Dec 2007 08:57:47 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	<linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-scsi@...r.kernel.org>, <rmk@....linux.org.uk>,
	<davem@...emloft.net>, <james.bottomley@...eleye.com>,
	<ralf@...ux-mips.org>
Subject: Re: [PATCH 2/2] scsi: Use new __dma_buffer to align sense buffer in scsi_cmnd

 > It's also incomplete as a fix because I don't see what guarantees the
 > buffer size will always exceed cache line size

There's a macro trick that adds a pad member after the buffer too, so
that it gets rounded up to the cacheline size:

 > +#define __dma_aligned	  	__attribute__((aligned(ARCH_MIN_DMA_ALIGNMENT)))
 > +#define __dma_buffer		__dma_buffer_line(__LINE__)
 > +#define __dma_buffer_line(line)	__dma_aligned;\
 > +				char __dma_pad_##line[0] __dma_aligned

So that part is OK at least.

 - R.
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