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Subject: Re: DMA using data buffer vmapped in kernel space
From: David Miller <davem@davemloft.net>
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From: Russell King - ARM Linux <linux@arm.linux.org.uk>
Date: Tue, 9 Mar 2010 09:14:03 +0000

> What you could do is prepare a patch to allow the firmware support to
> export a scatterlist via the struct firmware, and then use that with
> dma_map_sg().  Let's hope that the SPI interfaces support scatterlists.

It's so common to want a scatterlist from a vmalloc/vmap area
that a generic common helper is probably the best.

Just iterate over the vmalloc/vmap area using vmalloc_to_page()
to fill in the SG entries.