linux-kernel - Re: [PATCH 1/2 v3] dmaengine: at_hdmac: new driver for the Atmel AHB DMA Controller

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Date:	Sat, 18 Jul 2009 09:01:31 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
Cc:	maciej.sosnowski@...el.com, avictor.za@...il.com,
	linux-arm-kernel@...ts.arm.linux.org.uk, patrice.vilchez@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 v3] dmaengine: at_hdmac: new driver for the Atmel AHB 
	DMA Controller

On Fri, Jul 3, 2009 at 10:24 AM, Nicolas Ferre<nicolas.ferre@...el.com> wrote:
> This AHB DMA Controller (aka HDMA or DMAC on AT91 systems) is availlable on
> at91sam9rl chip. It will be used on other products in the future.
>
> This first release covers only the memory-to-memory tranfer type. This is the
> only tranfer type supported by this chip.  On other products, it will be used
> also for peripheral DMA transfer (slave API support to come).
>
> I used dmatest client without problem in different configurations to test it.
>
> Full documentation for this controller can be found in the SAM9RL datasheet:
> http://www.atmel.com/dyn/products/product_card.asp?part_id=4243
>
> Signed-off-by: Nicolas Ferre <nicolas.ferre@...el.com>
> ---
> v2 is here:
> http://lkml.org/lkml/2009/6/26/104
>
> v2 -> v3:
>  - initial number of descriptors to allocate for each channel raised to 64 and
>   is now a parameter
>  - ack-bit in descriptor flag comment synchronized with TXx9 dma driver
>  - atc_desc_get() when short on descriptors in pool: create one at a time
>  - allocation flag changed to GFP_ATOMIC in atc_desc_get()
>  - call to proper funtion while unmapping: use of new
>   DMA_COMPL_{SRC,DEST}_UNMAP_SINGLE flags
>  - call dma_run_dependencies() at the end of atc_chain_complete()
>

Looks good, but now I belatedly wonder if that GFP_ATOMIC should be
GFP_NOWAIT instead?  Do we really want to consume from the system
emergency pools for these allocations (a similar fix is need for
ioatdma and fsldma)?

Thanks,
Dan
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