[PATCH] Documentation: dmaengine: Add a documentation for the dma controller API

Maxime Ripard maxime.ripard at free-electrons.com
Fri Aug 1 01:57:07 PDT 2014

On Fri, Aug 01, 2014 at 10:00:10AM +0200, Lars-Peter Clausen wrote:
> On 07/31/2014 07:37 PM, Maxime Ripard wrote:
> >On Thu, Jul 31, 2014 at 06:54:11PM +0200, Lars-Peter Clausen wrote:
> >>On 07/31/2014 06:13 PM, Maxime Ripard wrote:
> >>[...]
> >>> From what you're saying, and judging from the drivers that already
> >>>implement it, can't it be moved directly to the framework itself ?
> >>>
> >>
> >>What exactly do you mean by moving it directly to the framework? The
> >>slave_caps API is part of the DMAengine framework.
> >
> >Not its implementation, which is defined by each and every driver,
> >while the behaviour of device_slave_caps is rather generic.
> >
> Do you mean something like adding a dma_slave_caps struct field to
> the DMA channel that gets initialized when the channel is created
> and then remove the callback? That makes some sense.

I was rather thinking into something like:
  - Splitting device_control into independant functions
  - Then, knowing if you support pause/resume/terminate is trivial:
    either you implement the callback, or you don't
  - Putting the supported width and direction into fields of struct
    dma_device, which can eventually be used by the framework to
    filter out invalid configurations before calling the relevant
  - That would then be trivial to get from the framework, without
    calling any callback

> I think the main reason why we use a callback right now is that in
> earlier revisions of the API it was possible to pass a slave_config
> and the result would be the capabilities of the DMA channel for this
> particular config. But this was dropped before the final version was
> merged upstream.

Ah, that would explain yes.


Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
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