linux-kernel - Re: DMA using data buffer vmapped in kernel space

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Message-ID: <20100309091403.GB5691@n2100.arm.linux.org.uk>
Date:	Tue, 9 Mar 2010 09:14:03 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Lin Mac <mkl0301@...il.com>
Cc:	Thomas Koeller <thomas@...ller.dyndns.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: DMA using data buffer vmapped in kernel space

On Tue, Mar 09, 2010 at 03:45:54PM +0800, Lin Mac wrote:
> I had encounter a similiar problem and I simply allocated a new
> buffer, copy the data, then DMA. It seems slow and stupid.
> 
> I'm wondering wether could I translate the vmap virt to phys(don't
> know how to yet), then use phys_to_virt to get the virt in
> direct-mapped memory region?
> 
> Is there other possible ways?

I think you need to talk to the firmware people... which is unfortunately
orphaned.

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.
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