linux-kernel - Re: [PATCH] MTD: atmel_nand: Add DMA support to access Nandflash

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Date:	Tue, 18 Jan 2011 11:42:07 +1300
From:	Ryan Mallon <ryan@...ewatersys.com>
To:	Hong Xu <hong.xu@...el.com>
CC:	linux-mtd@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	jamie@...ieiles.com, jacmet@...site.dk, nicolas.ferre@...el.com
Subject: Re: [PATCH] MTD: atmel_nand: Add DMA support to access Nandflash

On 01/18/2011 09:15 AM, Ryan Mallon wrote:
> On 01/17/2011 08:20 PM, Hong Xu wrote:
>> Some SAM9 chips have the ability to perform DMA between CPU and SMC controller.
>> This patch adds DMA support for SAM9RL, SAM9G45, SSAM9G46,AM9M10, SAM9M11.

I'm trying to patch this into a 2.6.33 kernel running on a custom
SAM9G45 based board, but I get a failure requesting the DMA channel:

root@...pper:~$ dmesg | grep -i dma
[    0.850000] atmel_nand atmel_nand: Failed to request DMA channel
[    0.860000] atmel_nand atmel_nand: No DMA support for NAND access.
[    1.530000] at_hdmac at_hdmac: Atmel AHB DMA Controller ( cpy slave ), 8 channels

It looks like the registration for the DMA controller happens after the
NAND driver probe and so the request is failing. I had a quick look, but
I can't see anything that would change this in more recent kernels. Any
ideas?

Also, I think you want to add the following for the atmel_nand Kconfig:
  select AT_HDMAC

or make the DMA parts of the driver ifdef CONFIG_AT_HDMAC (if the above
won't work for some reason) since you will get build errors on the
dmaengine functions otherwise.

~Ryan

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