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

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

Hello Vinod/Dan,

Please write your opinion.

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
>
> It seems that device_prep_interleaved_dma would not be able to handle
> such transfer.
>
> So, what I was thinking that to add following flags in enum dma_ctrl_flags.
>
> DMA_SRC_INC = (1 << 10),
> DMA_SRC_DEC = (2 << 10),
> DMA_SRC_FIX = (3 << 10),
> DMA_DST_INC = (1 << 12),
> DMA_DST_DEC = (2 << 12),
> DMA_DST_FIX = (3 << 12),
>
> Now we can use these flag in device_prep_dma_sg and this function can be
> implemented for generic cases.
>
> I think, the above modifications will not affect other's platform and
> should be acceptable.
>
> Whats your opinion?
>
> Regards
> Pratyush
>
> On 12/8/2011 1:20 PM, Viresh KUMAR wrote:
>> On 12/8/2011 1:07 PM, Vinod Koul wrote:
>>> You mean something like:
>>> struct dma_async_tx_descriptor *(*device_prep_dma_sg)(
>>> struct dma_chan *chan,
>>> struct scatterlist *dst_sg, unsigned int dst_nents,
>>> struct scatterlist *src_sg, unsigned int src_nents,
>>> unsigned long flags);
>>>
>>> Its already there, you need to implement in your driver :)
>>
>> Ok. I didn't knew it. :(
>>
>