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SubjectRe: [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<> 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:
>> Signed-off-by: Nicolas Ferre <>
>> ---
>> v2 is here:
>> 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
>> - 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

Nicolas Ferre

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