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

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Message-ID: <47CEF8C4B26E8C44B22B028A650E0EA9317AAD89@DBDE01.ent.ti.com>
Date:	Mon, 16 Jan 2012 10:59:34 +0000
From:	"Gupta, Ajay Kumar" <ajay.gupta@...com>
To:	Sergei Shtylyov <sshtylyov@...sta.com>,
	"Balbi, Felipe" <balbi@...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 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.

Currently AM33x/TI81x doesn't use cppi4.1 for Ethernet.

> 
> >>> 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. 

We can discuss more on this when we post design and API flow for review.

Regards,
Ajay
> 
> WBR, Sergei
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