[PATCH] dmaengine: sirf: add dmaengine_prep_slave_single/sg support

[Jassi Brar]

On 3 September 2013 17:38, Vinod Koul <vinod.koul at intel.com> wrote:
> On Tue, Sep 03, 2013 at 05:25:40PM +0530, Jassi Brar wrote:
>> > for example, if someone wants to do a 16Kbytes single transfer. how
>> > will interleaved dma set transfer length and interval between every
>> > row?
>> > if it sets the transfer length to 16KB directly, the dma hardware
>> > might not support such long a transfer at all.
>> > so it might want to set as two 8KB transfer without interval between them.
>> > 0~8KB                empty interval
>> > 8KB-16KB          empty interval
>> > or four 4KB transfer as
>> > 0~4KB                empty interval
>> > 4KB-8KB          empty interval
>> > 8KB-12KB          empty interval
>> > 12KB-16KB          empty interval
>> >
>> > the problem is we don't know the hardware limitation of every dma
>> > controllers for transferring length of each row.
>> >
>> A client is only interested in transferring the total amount data and
>> if/when it wants notified. How the dma controller divides the big
>> transfer, shouldn't matter to the client. In fact it would be bad for
>> a client to care about the working of a dma controller.
>> IOW, the 16KB transfer could be divided into 4 parts by the dmac that
>> supports max 4KB transfers, into 8 parts if max is 2KB and so on...
>> the client shouldn't care.
> That is also a correct approach. I agree that dma driver should be able to
> handle any lengths and split that to multiple descriptors.
>
> But I think in interleaved API, clients should know the capablity otherwise dma
> driver will have redo the whole list again...
>
I am not sure if the clients should do the mapping from arbitrary data
pattern onto how the dmac is to be programmed. The client is no more
generic (it just passes dmac specific data in a generic way), and the
approach also entails yet another api for dmacs to express their
capability.

As we know, the interleaved api was meant for clients to express
arbitrary data arrangement in memory. It's not for clients passing
transfer info in dmac specific format.

-jassi