linux-kernel - Re: [PATCH] fsldma: add support to 36-bit physical address

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Message-ID: <AANLkTine--kry0c0n87WOqYyi3AQOb2KnmNRs-MeXcQt@mail.gmail.com>
Date:	Tue, 21 Sep 2010 16:43:12 -0500
From:	Timur Tabi <timur.tabi@...il.com>
To:	Scott Wood <scottwood@...escale.com>
Cc:	Kumar Gala <galak@...nel.crashing.org>, dan.j.williams@...el.com,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fsldma: add support to 36-bit physical address

On Tue, Sep 21, 2010 at 4:34 PM, Scott Wood <scottwood@...escale.com> wrote:

> This doesn't control allocation (it probably should with
> dma_alloc_coherent, though I don't see it in the code), it controls
> whether swiotlb will create a bounce buffer -- defeating the point of
> using DMA to accelerate a memcpy.

But it would do that only for the 'dev' used in the dma_set_mask()
call.  That dev is only used here:

	chan->desc_pool = dma_pool_create("fsl_dma_engine_desc_pool",
					  chan->dev,
					  sizeof(struct fsl_desc_sw),
					  __alignof__(struct fsl_desc_sw), 0);

Since we don't DMA the descriptors themselves, I just don't see how
this patch does anything.

-- 
Timur Tabi
Linux kernel developer at Freescale
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