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

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

On 12/15/2011 10:36 AM, Koul, Vinod wrote:
>>
>> Hello Vinod/Dan,
>>
>> Please write your opinion.
> I am on vacation, but will reply briefly here, more next week

Thanks for your quick reply.

>>
>> Regards
>> Pratyush
>>
>> On 12/14/2011 12:17 PM, Pratyush Anand wrote:
>>> Hello Vinod/Dan,
>>>
>>> In continuation to the scatter/gather requirement:
>>> We might need some generic transfer where source and destination
>>> address may be overlapped and also gap between two chunk of source and
>>> destination might not be same.
>>>
>>> For examaple,
>>> Transfer size is - -0x4000
>>> Our Src is something like this:
>>> 0x1000 -- 0x2000
>>> 0x3000 -- 0x5000
>>> 0x6000 -- 0x7000
>>>
>>> and dst is something like this:
>>> 0x6000 -- 0x8000
>>> 0x9000 -- 0xB000
> So why can't it be split like:
> 0x1000--0x2000 =>  0x6000 --0x7000
> 0x3000 -- 0x4000 =>  0x7000 - 0x8000
> 0x4000 -- 0x5000 =>  0x9000 - 0xA000
> 0x6000 -- 0x7000 =>  0xA000 - 0xB000
>
> 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.

Regards
Pratyush

> --
> ~Vinod