From: Matt Porter <mporter@kernel.crashing.org>
To: Bret Indrelee <Bret.Indrelee@qlogic.com>
Cc: Linux PPC Embedded mailing list <linuxppc-embedded@lists.linuxppc.org>
Subject: Re: Any restrictions on DMA address boundry?
Date: Mon, 22 Sep 2003 09:59:52 -0700 [thread overview]
Message-ID: <20030922095952.A31727@home.com> (raw)
In-Reply-To: <Pine.LNX.4.44.0309221006580.30267-100000@spider.ancor.com>; from Bret.Indrelee@qlogic.com on Mon, Sep 22, 2003 at 10:13:26AM -0500
On Mon, Sep 22, 2003 at 10:13:26AM -0500, Bret Indrelee wrote:
>
> Are there alignment restrictions on the address boundry your can
> start a DMA with when using the pci_map_single() / pci_unmap_single()
> calls?
>
> For some reason, I thought they had to be cache line aligned, but when
> I went back through the documentation I couldn't find any such
> restriction.
cache line alignment is an unwritten requirement that hasn't yet been
addressed in DMA-mapping.txt. Unfortunately, kmalloc() doesn't
guarantee this so it's necessary to overallocate and align.
You can use L1_CACHE_BYTES for this.
Roland Dreier had a patch which added a little helper for this
stuff as well as docs. Unfortunately, it's been dropped on the
floor until somebody with interest and time in non-coherent
platforms picks it up. http://lwn.net/Articles/2482/
-Matt
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2003-09-22 16:59 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-09-22 15:13 Any restrictions on DMA address boundry? Bret Indrelee
2003-09-22 16:59 ` Matt Porter [this message]
2003-09-25 17:56 ` Roland Dreier
2003-09-25 18:15 ` Bret Indrelee
2003-09-25 18:26 ` Roland Dreier
2003-09-25 20:54 ` Eugene Surovegin
2003-09-25 19:56 ` Matt Porter
2003-09-25 20:20 ` Bret Indrelee
2003-09-25 20:55 ` Matt Porter
2003-09-25 21:27 ` Bret Indrelee
2003-09-25 20:25 ` Eugene Surovegin
2003-09-25 20:32 ` Bret Indrelee
2003-09-25 20:57 ` Matt Porter
2003-09-25 20:41 ` Matt Porter
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