Re: RFC: usb: musb: Adding CPPI4.1 DMA driver under drivers/dma

[Sergei Shtylyov]

Hello.

On 14-01-2012 0:10, Felipe Balbi wrote:

> > > CPPI4.1 (Communication Port Programming Interface) is a TI specific DMA
> > > controller used in multiple TI platform such as AM33x, DA8x, AM35x, TI81x.
> > > The DMA engine is mainly used by musb controller on above platform.

> >     There are (at least out of tree) platforms using CPPI 4.1 for Ethernet.

> if they are out of tree, I'm sorry but we don't care about them. If they
> are in tree, then that needs to be sorted out on the same patchset.

   I'm not sure if Puma-5 is the only one using CPPI 4.1 for Etherhet, and 
not some new platfroms introduced just now like AM33x/TI81x.

> > > It would involve changes in existing musb driver also for which current
> > > plan is to maintain the compatibility of non-CPPI4.1 DMA in musb driver.

> >     I didn't quite understand this part...

> how come ? What he's saying is that while moving cppi-dma.c to

   How come we are taling of cppi-dma.c at all? It's CPPI 3.0 driver having 
nothing in common with CPPI 4.1.

> drivers/dma he will not move all the other dma engines (Inventra, OMAP,
> TUSB-over-GPMC, etc).

> > > The task is planned to be spitted into below subtasks.

> > > (1) Post RFC on the API details, changes envisaged in musb driver and other
> > > challenges

> >     First of all, I foresee changes in drivers/dma/ to cope with the
> > entity in CPPI 4.1 called the queue manager (there's also buffer
> > manager but it wasn't implemented on DA8xx, so I didn't design any
> > API for it).

> that's why the kernel is open source, right ? If we need to improve the
> framework so that it understands other types of DMAs, so be it.

   I just foresee difficulties here.

WBR, Sergei
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