linux-kernel - Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver

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Date:	Thu, 8 Sep 2011 10:18:32 +0800
From:	Barry Song <21cnbao@...il.com>
To:	"Koul, Vinod" <vinod.koul@...el.com>
Cc:	"jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	DL-SHA-WorkGroupLinux <workgroup.linux@....com>
Subject: Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver

2011/9/8 Koul, Vinod <vinod.koul@...el.com>:
> On Thu, 2011-09-08 at 00:46 +0800, Barry Song wrote:
>> Hi Vinod,
>> thanks for your quick feedback.
>>
>> 2011/9/8 Koul, Vinod <vinod.koul@...el.com>:
>> > On Tue, 2011-09-06 at 22:41 -0700, Barry Song wrote:
>> >> From: Rongjun Ying <rongjun.ying@....com>
>> >
>> >> +config SIRF_DMA
>> >> +     tristate "CSR SiRFprimaII DMA support"
>> >> +     depends on ARCH_PRIMA2
>> >> +     select DMA_ENGINE
>> >> +     help
>> >> +       Enable support for the CSR SiRFprimaII DMA engine.
>> > How different is it from the other primacell based DMA drivers, and why
>> > wouldn't it make sense to use/modify one of them?
>>
>> it is much different with primacell based DMA like pl080, pl330.
>> prima2 has a self-defined DMAC IP. basically it is a 2D mode dma with
>> two scales X and Y and direct way to start and stop DMA.
>> every channel has fixed function to serve only one perpheral. so you
>> find we have a filter id.
> okay, what do you mean by 2D mode? Is it similar to what TI folks, Linus
> W and Jassi Brar posted RFC's on?

In SiRFprimaII 2-D DMA, the system memory space is interpreted
as a 2-D layout instead of a linear 1-D layout. More specifically, the
system memory can be considered as
multiple data lines. The length of the data line is determined by the
user-selected DMA_WIDTH register.
The user can specify a data window that the user wants to access using
four parameters:
■ Start address
■ X length
■ Y length
■ Width

The idea of a 2-D DMA is shown in figure 2d-dma.png attached.

If you specifies the Y length as 0 or the X length equals to the DMA
width, then this 2-D DMA reduces to
1-D. If the user configures the X length greater than the DMA width,
then the extra data is wrapped around
to the next data line, this may corrupt the DMA transfer for
multiple-line 2-D DMA. If this is a 1-D DMA, then
there is no issue. The attached diagram 2d-dma2.png shows the
wrap-around of the extra data in case the X length
greater than DMA width.

Thanks
barry

Download attachment "2d-dma.PNG" of type "image/png" (16675 bytes)

Download attachment "2d-dma2.PNG" of type "image/png" (9836 bytes)