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

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Message-ID: <CABb+yY3F+DMn2SxeO0chjpiMBkgLvSK5EVYMdhQsfQoZNZ4_7Q@mail.gmail.com>
Date:	Thu, 8 Sep 2011 10:55:24 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Barry Song <21cnbao@...il.com>
Cc:	"Koul, Vinod" <vinod.koul@...el.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>,
	"workgroup.linux@....com" <workgroup.linux@....com>,
	"rongjun.ying@....com" <rongjun.ying@....com>,
	"Baohua.Song@....com" <Baohua.Song@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver

On Thu, Sep 8, 2011 at 8:47 AM, Jassi Brar <jassisinghbrar@...il.com> wrote:
> On Thu, Sep 8, 2011 at 7:42 AM, Barry Song <21cnbao@...il.com> wrote:
>
>>>> 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.
>
> Sorry, the role of DMA_WIDTH is not clear to me yet.
> In which case the user _must_ set {xlen > width} ?
>
Perhaps 2d-dma.PNG is inaccurate - it shouldn't depict any deltaX.
Doesn't xlen and width always start together ? If no, please don't read ahead.

According to figures, {xlen > width} is to be set _only_ when a transfer
is divided into _exactly_ two chunks separated by gap _exactly_
equal to length of the second chunk (an extremely rare case).

Anyways, every case can be easily expressed using the generic api
I proposed. See 'struct xfer_template' in https://lkml.org/lkml/2011/8/12/128

Roughly speaking, the following should be done...
Client driver :-
**************
For a 'Rectangular' transfer (2d-dma.PNG) :-
      xfer_template.numf = Ylen;  /* height of rectangle */
      xfer_template.frame_size = 1;
      xfer_template.sgl[0].size = Xlen; /* width of rectangle */
      xfer_template.sgl[0].icg = start_addr_Y(n) - end_addr_Y(n-1);

For the "A Line and some" transfer (2d-dma2.PNG) :-
      xfer_template.numf = 1;
      xfer_template.frame_size = 2;
      xfer_template.sgl[0].size = xlen1; /* a line */
      xfer_template.sgl[1].size = xlen2;  /* and some */
      xfer_template.sgl[0].icg = start_addr_Y(n) - end_addr_Y(n-1);
      xfer_template.sgl[1].icg = 0; /* doesn't matter */

DMAC driver :-
***************
      if (xfer_template.frame_size == 1) {
           /* rectangle */
           schan->xlen = xfer_template.sgl[0].size;
           schan->width = schan->xlen + xfer_template.sgl[0].icg;
      } else if (xfer_template.frame_size == 2 &&
                  xfer_template.numf == 1 &&
                  xfer_template.sgl[1].size == xfer_template.sgl[0].icg){
           /* a line and some */
           schan->xlen = xfer_template.sgl[0].size +  xfer_template.sgl[1].size.
           schan->width = xfer_template.sgl[0].size;
      } else {
           /* _Hardware_ doesn't support the transfer as such. *
           return -EINVAL;
      }
      schan->ylen = xfer_template.numf /* -1? */;
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