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

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Message-ID: <20120113201205.GK3133@legolas.emea.dhcp.ti.com>
Date:	Fri, 13 Jan 2012 22:12:07 +0200
From:	Felipe Balbi <balbi@...com>
To:	Greg KH <greg@...ah.com>
Cc:	"Gupta, Ajay Kumar" <ajay.gupta@...com>,
	"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

On Fri, Jan 13, 2012 at 10:09:32AM -0800, Greg KH wrote:
> On Fri, Jan 13, 2012 at 10:40:50AM +0000, Gupta, Ajay Kumar wrote:
> > Hi,
> > 
> > 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.
> > 
> > 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.
> > Refer the discussions at [1] for more details.
> > 
> > [1] http://marc.info/?l=linux-usb&m=125087318308323
> > 
> > The new implementation of the CPPI4.1 DMA slave driver will be in the
> > drivers/dma folder, complying to dmaengine framework.
> > 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. 
> > 
> > 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
> > 
> > (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.
> 
> First off, don't highjack threads (you responded to a linux-usb thread
> here, get a better email client please.)
> 
> Second, that sounds fine, please post patches.

I'm with Greg here, please post patches.

What I suggest is:

- first create a dma-engine.c file on drivers/usb/musb which will simply
  translate dmaengine into the MUSB-specific API.
  	this will allow us to slowly convert other platforms without
	breaking the legacy stuff.

- Then move CPPI to drivers/dma

- Test it all out ;-)

-- 
balbi

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