From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>
Subject: Re: [PATCH 2/2] dmaengine: Add support for the Analog Devices AXI-DMAC
 DMA controller
Date: Wed, 19 Aug 2015 18:55:34 +0200
Message-ID: <55D4B506.9010707@metafoo.de>
References: <1438076286-21164-1-git-send-email-lars@metafoo.de> <1438076286-21164-2-git-send-email-lars@metafoo.de> <20150819163203.GF13546@localhost>
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To: Vinod Koul <vinod.koul-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>, Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>, Ian Campbell <ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>, Kumar Gala <galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, dmaengine-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-Id: devicetree@vger.kernel.org

On 08/19/2015 06:32 PM, Vinod Koul wrote:
> On Tue, Jul 28, 2015 at 11:38:06AM +0200, Lars-Peter Clausen wrote:
>> +	active = axi_dmac_active_desc(chan);
>> +	if (!active)
>> +		return;
>> +
>> +	if (active->cyclic) {
>> +		vchan_cyclic_callback(&active->vdesc);
>> +	} else {
>> +		while (active &&
> do you need to check this, you did that few lines back?

It gets overwritten in the loop.

[...]
> 
>> +static struct dma_async_tx_descriptor *axi_dmac_prep_slave_sg(
>> +	struct dma_chan *c, struct scatterlist *sgl,
>> +	unsigned int sg_len, enum dma_transfer_direction direction,
>> +	unsigned long flags, void *context)
>> +{
>> +	struct axi_dmac_chan *chan = to_axi_dmac_chan(c);
>> +	struct axi_dmac_desc *desc;
>> +	struct scatterlist *sg;
>> +	unsigned int i;
>> +
>> +	if (direction != chan->direction)
> 
> are the channels unidirectional

yes.

> 
>> +		return NULL;
>> +
>> +	desc = axi_dmac_alloc_desc(sg_len);
>> +	if (!desc)
>> +		return NULL;
>> +
>> +	for_each_sg(sgl, sg, sg_len, i) {
>> +		if (!axi_dmac_check_addr(chan, sg_dma_address(sg)) ||
>> +		    !axi_dmac_check_len(chan, sg_dma_len(sg))) {
>> +			kfree(desc);
>> +			return NULL;
>> +		}
>> +
>> +		if (direction == DMA_DEV_TO_MEM)
>> +			desc->sg[i].dest_addr = sg_dma_address(sg);
>> +		else
>> +			desc->sg[i].src_addr = sg_dma_address(sg);
> where is device side programming ?

in the start_transfer() function.

> 
>> +
>> +	if (axi_dmac_dest_is_mem(chan) && axi_dmac_src_is_mem(chan))
>> +		chan->direction = DMA_MEM_TO_MEM;
>> +	else if (!axi_dmac_dest_is_mem(chan) && axi_dmac_src_is_mem(chan))
>> +		chan->direction = DMA_MEM_TO_DEV;
>> +	else if (axi_dmac_dest_is_mem(chan) && !axi_dmac_src_is_mem(chan))
>> +		chan->direction = DMA_DEV_TO_MEM;
>> +	else
>> +		chan->direction = DMA_DEV_TO_DEV;
> 
> ok this seems to answer my other question but is this something we are
> specifying in SW or capability of a channel?

That's a capability of the hardware.
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