Re: RFC: usb: musb: Changes proposed for adding CPPI4.1 DMA

[Sergei Shtylyov]

Hello.

On 02-02-2012 8:57, Gupta, Ajay Kumar wrote:

> > > > > As a next step to dma-engine based cppi4.1 driver implementation
> > > > > this RFC has the overview of changes in the musb driver.
> > > > > RFC on CPPI slave driver changes will follow next.

> > > > > Overview of changes in the musb driver
> > > > > ======================================

> > > > > 1)Add a dma-engine.c file in the drivers/usb/musb folder
> > > > > 2)This file will host the current musb dma APIs and translates them to
> > > > >      dmaengine APIs.
> > > > > 3)This will help to keep the changes in drivers/usb/musb/musb* files
> > > > >      minimal and also to retain compatibility other DMA (Mentor etc.)
> > > > >      drivers which are yet to be moved to drivers/dma
> > > > > 4)drivers/usb/musb/dma-engine.c, will wrap the dmaengine APIs to
> > > > >      make existing musb APIs compatible.
> > > > > 5)drivers/usb/musb/dma-engine.c file will implement the filter
> > > > >      functions and also implement .dma_controller_create (allocates
> > > > >      &    provides "dma_controller" object) and .dma_controller_delete
> > > > > 6)CPPI4.1 DMA specific queue and buffer management will be internal
> > > > >      to slave CPPI DMA driver implementation.

> > > >       You mean drivers/dma/ driver?

> > > yes.

> > > > I think you are forgotting that CPPI 4.1 MUSB
> > > > has some registers controlling DMA/interrupts beside those of CPPI 4.1
> > > > controller and MUSB core itself. How do they fit in your scheme?

> > > We have been discussing on how to handle these in slave driver and

> >      These certainly cannot be handled in the slave driver because the
> > registers are different for every controller implementation and, the
> > main thing, they don't belong to CPPI 4.1 as such.

> Felipe suggested to use device tree for differences in register maps
> among different platforms.

   I don't see how the device tree would magically help here.

> I do see issues in reading wrapper interrupt status register and then
> calling musb_interrupt() [defined inside musb_core.c] from slave driver.

> > > would post our proposal in RFC for slave driver design. Do you have
> > > any proposal?

> >      I think this will need hooks from dma-engine.c to the glue layers. I
> > was going to implement such in my version of MUSB CPPI 4.1 driver (in order
> > to also support AM35x) but lacked time.

> That would mean a change in current drivers/dma API.

   No, it doesn't. I'm proposing hooks from dma-engine.c which is situated in 
drivers/usb/musb/ if I got you right. It just means that the calls to 
dma-engine.c as MUSB DMA driver won't map to the calls to the DMA slave driver 
as directly as you've presented before.

> Ajay

> > > Regards,
> > > Ajay

WBR, Sergei
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