Re: [RFC] dmaengine: add new api for preparing simple slave transfer

[Jassi Brar]

On Thu, Jun 9, 2011 at 6:09 PM, Raju, Sundaram <sundaram@xxxxxx> wrote:

> Generic buffer description:
> A generic buffer can be split into number of frames which contain number of chunks inside them. The frames need not be contiguous, nor do the chunks inside a frame.
>
> Â Â Â Â-------------------------------------------------------------------
> Â Â Â Â| Chunk 0 |ICG| Chunk 1 |ICG| ... |ICG| Chunk n | Â Â Â Frame 0
> Â Â Â Â-------------------------------------------------------------------
>    Â|            Inter Frame Gap           |
> Â Â Â Â-------------------------------------------------------------------
> Â Â Â Â| Chunk 0 |ICG| Chunk 1 |ICG| ... |ICG| Chunk n | Â Â Â Frame 1
> Â Â Â Â-------------------------------------------------------------------
>    Â|            Inter Frame Gap           |
> Â Â Â Â-------------------------------------------------------------------
> Â Â Â Â| Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â ........ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â|
> Â Â Â Â-------------------------------------------------------------------
>    Â|            Inter Frame Gap           |
> Â Â Â Â-------------------------------------------------------------------
> Â Â Â Â| Chunk 0 |ICG| Chunk 1 |ICG| ... |ICG| Chunk n | Â Â Â Frame m
> Â Â Â Â-------------------------------------------------------------------

IIUC the above figure, the work done by DMA controller remains the
same, either by
passing this as a transfer of the new type or as a normal sg-list  - unless
the DMAC driver attempts to reorder the transfers or the DMAC h/w
natively supports
some form of sg-list.
For DMACs, that have no special support, different representation
wouldn't make a
difference.
And if the DMAC does support the kind of fancy scatter-gather, it
should be possible for
the dma api driver to analyze the submitted 'normal' sg-list and
program the transfers at one go.
Besides, it should be possible to have a 'template' sequence of
requests prepared
already because usually, for above mentioned scenario, the parameters
don't change across
items in a list.
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