[PATCH 18/18] fsmc/nand: Add DMA support

[Vipin Kumar]

On 3/7/2012 9:39 PM, Linus Walleij wrote:
> On Wed, Mar 7, 2012 at 12:31 PM, Vipin Kumar<vipin.kumar at st.com>  wrote:
>
>> The fsmc_nand driver uses cpu to read/write onto the device. This is inefficient
>> because of two reasons
>> - the cpu gets locked on AHB bus while reading from NAND
>> - the cpu is unnecessarily used when dma can do the job
>>
>> This patch adds the support for accessing the device through DMA
>
> Please elaborate a bit on how this is done, because I think it's new
> stuff.
>
> It appears that the FSMC is not like a slave device, i.e. not taking a
> stream of bytes. Instead you use the memcpy() portions of the
> dmaengine API to move data in/out of the flash pages to the
> page currently handled by the controller.
>

Yes, that's right. memcpy portions of dmaengine API are being used to 
move the data in/out of flash pages

> Is this correct? I think it's pretty interesting since it's a new usecase
> for in-kernel memcpy() which (AFAIK) has so far only been used
> to accelerate network packet copying (correct me if wrong!).
>

I also saw the same use case in drivers/ata/pata_arasan_cf.c. Have a 
look at dma_xfer routine in this file

Regards
Vipin