linux-kernel - Re: [PATCH V4 3/5] dmaengine/dw_dmac: Divide one sg to many desc, if sg len is greater than DWC_MAX

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Date:	Mon, 09 May 2011 11:17:21 +0530
From:	"Koul, Vinod" <vinod.koul@...el.com>
To:	viresh kumar <viresh.kumar@...com>
Cc:	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Armando VISCONTI <armando.visconti@...com>,
	Shiraz HASHIM <shiraz.hashim@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"viresh.linux@...il.com" <viresh.linux@...il.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>
Subject: Re: [PATCH V4 3/5] dmaengine/dw_dmac: Divide one sg to many desc,
 if sg len is greater than DWC_MAX_COUNT

On Mon, 2011-05-09 at 11:33 +0530, viresh kumar wrote:
> On 05/09/2011 10:50 AM, Koul, Vinod wrote:
> >> > @@ -695,9 +695,15 @@ dwc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
> >> >  		reg = dws->tx_reg;
> >> >  		for_each_sg(sgl, sg, sg_len, i) {
> >> >  			struct dw_desc	*desc;
> >> > -			u32		len;
> >> > -			u32		mem;
> >> > +			u32		len, dlen, mem;
> >> >  
> >> > +			mem = sg_phys(sg);
> >> > +			len = sg_dma_len(sg);
> >> > +			mem_width = 2;
> > hardcoding mem_width doesn't make sense, you should take this from input
> > params
> 
> Firstly, this change is not introduced in this patch, i have just rearranged this.
> So, will send separate patch if this change is required.
> 
> Secondly, peripheral width is taken from chan->private. And by 2 for mem_width,
> we meant word-by-word here. Shouldn't we always try word-by-word here?
> How should we pass width for memory?
Ah, then there is another todo for this driver. Move from chan->private
to DMA_SLAVE_CONFIG.

struct dma_slave_config has dedicated fields for both source and
destination widths, src_addr_width & dst_addr_width please use them...
You should pass this structure to device control API as:
dmaengine_device_control(
	chan, DMA_SLAVE_CONFIG, (unsigned long)&slave_config);

-- 
~Vinod

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