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

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Message-ID: <1315518378.6638.2.camel@vkoul-mobl4>
Date:	Fri, 09 Sep 2011 03:16:18 +0530
From:	Vinod Koul <vkoul@...radead.org>
To:	Jassi Brar <jassisinghbrar@...il.com>
Cc:	vinod.koul@...el.com, Barry Song <21cnbao@...il.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"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>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver

On Thu, 2011-09-08 at 10:55 +0530, Jassi Brar wrote:
> 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? */;
Looks like Jassi got a user for his proposed API. I am not sure whats
going on with TI folks, they never showed up here @LPC.


-- 
~Vinod Koul
Intel Corp.

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