Re: dmaengine/Query: What about scatter/gather for mem to mem transfers.

[Pratyush Anand <pratyush.anand@st.com>]

On 1/2/2012 5:05 PM, Vinod Koul wrote:
> On Tue, 2011-12-20 at 15:45 +0530, Pratyush Anand wrote:
>> >  On 12/20/2011 2:51 PM, Vinod Koul wrote:
>>> >  >  On Thu, 2011-12-15 at 12:26 +0530, Pratyush Anand wrote:
>>>>>> >  >>>>  That way existing mechanism would work well for you.
>>>>>> >  >>>>  You need to split the chunks properly, which is what dma would do
>>>> >  >>  anyway
>>>>>> >  >>>>
>>>>> >  >>>
>>>>> >  >>>  Yes, they can be split like this, but then splitting onus will go on
>>>> >  >>  dma
>>>>> >  >>>  user driver, and so there would be replication of similar logic at
>>>>> >  >>>  several places. Therefore, I was thinking to make device_prep_dma_sg
>>>> >  >>  as
>>>>> >  >>>  generic by adding these flags.
>>> >  >  Well I am not sure how adding flags handles this?
>> >
>> >  device_prep_dma_sg has last argument as flags. dma user driver can pass
>> >  information about inc/dec of src/dst in this flag, which can be used by
>> >  the dma driver. I have put one such implementation at the end of mail.
> with the split pre-done would we need to do this, hence the referred
> implementation.
>

even with pre-done, some flag in this function will be needed. Because 
HW also need o know whether to src and dst are in incrementing or 
decrementing order.