From: Matt Porter <mporter@kernel.crashing.org>
To: Eugene Surovegin <ebs@ebshome.net>
Cc: Matt Porter <mporter@kernel.crashing.org>,
Bret Indrelee <Bret.Indrelee@qlogic.com>,
Roland Dreier <roland@topspin.com>,
Linux PPC Embedded mailing list
<linuxppc-embedded@lists.linuxppc.org>
Subject: Re: Any restrictions on DMA address boundry?
Date: Thu, 25 Sep 2003 13:41:12 -0700 [thread overview]
Message-ID: <20030925134112.A17028@home.com> (raw)
In-Reply-To: <5.1.0.14.2.20030925131735.03abfab8@mail.ebshome.net>; from ebs@ebshome.net on Thu, Sep 25, 2003 at 01:25:00PM -0700
On Thu, Sep 25, 2003 at 01:25:00PM -0700, Eugene Surovegin wrote:
> At 12:56 PM 9/25/2003, Matt Porter wrote:
> >When a buffer is allocated using the allowed methods (as defined in
> >DMA-mapping.txt) to obtain memory for use in DMA, there is
> >no guarantee that the buffer is cacheline aligned.
>
> Hmm, I don't think this is true.
>
> DMA-mapping.txt explicitly states that pci_alloc_consistent() returns
> aligned memory buffer:
>
> " ... The cpu return address and the DMA bus master address are both
> guaranteed to be aligned to the smallest PAGE_SIZE order which
> is greater than or equal to the requested size. This invariant
> exists (for example) to guarantee that if you allocate a chunk
> which is smaller than or equal to 64 kilobytes, the extent of the
> buffer you receive will not cross a 64K boundary..."
>
> I think it's safe to assume that PAGE_SIZE alignment also guarantees
> cacheline alignment for all existing CPUs.
Yes, that's correct. However, I was alluding to kmalloc()'ed
buffers that are to be used with the streaming calls in the
DMA API.
-Matt
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
prev parent reply other threads:[~2003-09-25 20:41 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
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 [this message]
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