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

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Date:	Sun, 15 Jan 2012 01:24:01 +0400
From:	Sergei Shtylyov <sshtylyov@...sta.com>
To:	balbi@...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

Hello.

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.

>>> 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.

WBR, Sergei
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