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

[Gupta, Ajay Kumar]

Hi,
> 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 don't know this as of now as need to explore DT and see if that would help.

> 
> > 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.

got it but passing the interrupt status from slave driver will be difficult
on am18x as there is single irq line for musb in AM18x whereas ti81xx and
AM335x has two interrupt line one for CPPI DMA and one for each mentor controller.

Ajay
> 
> > Ajay
> 
> >>> Regards,
> >>> Ajay
> 
> WBR, Sergei
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