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Date: Mon, 20 Dec 2004 11:43:59 +0300
From: "Gleb O. Raiko" <raiko@niisi.msk.ru>
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To: wuming <wuming@ict.ac.cn>
CC: linux-mips@linux-mips.org
Subject: Re: problem about dma
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.