linux-kernel - RE: RFC: usb: musb: Adding CPPI4.1 DMA driver under drivers/dma

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Date:	Mon, 16 Jan 2012 10:56:11 +0000
From:	"Gupta, Ajay Kumar" <ajay.gupta@...com>
To:	Sergei Shtylyov <sshtylyov@...sta.com>
CC:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: RFC: usb: musb: Adding CPPI4.1 DMA driver under drivers/dma

Hi,
> On 01/13/2012 01:40 PM, Gupta, Ajay Kumar 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.
> 
> > Earlier version of the driver was submitted by Sergei Shtylyov at [1]
> but
> > was not merged due to disagreement on the location of driver in
> kernel.
> 
>     To be precise, TI requested pulling out already queued (to
> arch/arm/common/)
> CPPI 4.1 driver from RMK's patch system without even notifying me. At
> least that
> was RMK's version...
> 
> > Refer the discussions at [1] for more details.
> 
> > [1] http://marc.info/?l=linux-usb&m=125087318308323
> 
>     Unfortunately, that's not all of the discussion of interest.
> 
> > The new implementation of the CPPI4.1 DMA slave driver will be in the
> > drivers/dma folder, complying to dmaengine framework.
> 
>     Has there been any work in this direction done yet?

Currently we are working on design flow and API details which will be posted
first for review.

Ajay
> 
> > 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...
> 
> > 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).
> 
> > (2) Implement and post RFC for the CPPI4.1 DMA driver and changes
> needed in
> > musb driver.
> 
> > Let me know if you have any thoughts/comments on this.
> 
> > Regards,
> > Ajay
> 
> WBR, Sergei

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