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

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Message-ID: <129600E5E5FB004392DDC3FB599660D7AF6D5C9A@irsmsx504.ger.corp.intel.com>
Date:	Wed, 22 Jul 2009 14:35:06 +0100
From:	"Sosnowski, Maciej" <maciej.sosnowski@...el.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
CC:	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.arm.linux.org.uk" 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"avictor.za@...il.com" <avictor.za@...il.com>,
	"patrice.vilchez@...el.com" <patrice.vilchez@...el.com>
Subject: RE: [PATCH 1/2 v3] dmaengine: at_hdmac: new driver for the Atmel
 AHB 	DMA Controller

Nicolas Ferre wrote:
> 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...

I think it's a good plan.
I will prepare similar patch on allocation flags for ioatdma.

For this v3 patch:

Acked-by: Maciej Sosnowski <maciej.sosnowski@...el.com>

Regards,
Maciej--
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