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

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Date:	Tue, 21 Jul 2009 10:33:28 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Dan Williams <dan.j.williams@...el.com>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org
CC:	maciej.sosnowski@...el.com, avictor.za@...il.com,
	patrice.vilchez@...el.com
Subject: Re: [PATCH 1/2 v3] dmaengine: at_hdmac: new driver for the Atmel
 AHB 	DMA Controller

Dan Williams :
> 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)?

Seems sensible indeed but I know little about allocation flags.

What do you think about including the driver and then building a patch
that fixes this flag in all allocation functions at a time.
It may add exposure to this modification and maybe encourage people to
react...

Regards,
-- 
Nicolas Ferre

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