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Re: problem about dma

To: wuming <wuming@ict.ac.cn>
Subject: Re: problem about dma
From: "Gleb O. Raiko" <raiko@niisi.msk.ru>
Date: Mon, 20 Dec 2004 11:43:59 +0300
Cc: linux-mips@linux-mips.org
In-reply-to: <001501c4e646$7f676c00$6f64a8c0@spark>
Organization: NIISI RAN
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <001501c4e646$7f676c00$6f64a8c0@spark>
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wuming wrote:
Before the dma transfer, pci_map_sg will map the memory space covered by 
sg_table,
and it will flush and invalidate cache indexed by that memory space.
After the dma transfer, pci_unmap_sg also needs to be called to flush and 
invalidate
the same cache. But I do not know why the second flush will be demanded.
I think that in the interval between the two flush, there would be nothing to 
access
the memory covered by the dma. But it is not the case.
I want to know what can access that memory and I need some help.

In 2.4, memcpy's prefetch may (and, in practice, do, no smiles, it cost me a lot of time to realize) access that memory. I though it has been fixed in 2.6 someday.

Regards,
Gleb.

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