linux-kernel - Re: [PATCH 3/6] dma: Add a jz4740 dmaengine driver

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Date:	Fri, 24 May 2013 11:24:53 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Ralf Baechle <ralf@...ux-mips.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Maarten ter Huurne <maarten@...ewalker.org>,
	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	alsa-devel@...a-project.org
Subject: Re: [PATCH 3/6] dma: Add a jz4740 dmaengine driver

On Fri, May 24, 2013 at 07:58:04AM +0200, Lars-Peter Clausen wrote:
> This one needs both.
> 
> >> +	jzcfg.mode = JZ4740_DMA_MODE_SINGLE;
> >> +	jzcfg.request_type = config->slave_id;
> >> +
> >> +	chan->config = *config;
> >> +
> >> +	jz4740_dma_configure(chan->jz_chan, &jzcfg);
> >> +
> >> +	return 0;
> > You are NOT use src_addr/dstn_addr? How else are you passing the periphral
> > address?
> I'm saving the whole config, which will later be used to retrieve the source or
> dest address.
well I missed that and it is a bad idea. You dont know when client has
freed/thrown the pointer so copy this instead..

> 
> >> +}
> [...]
> >> +static int jz4740_dma_alloc_chan_resources(struct dma_chan *c)
> >> +{
> >> +	struct jz4740_dmaengine_chan *chan = to_jz4740_dma_chan(c);
> >> +
> >> +	chan->jz_chan = jz4740_dma_request(chan, NULL);
> >> +	if (!chan->jz_chan)
> >> +		return -EBUSY;
> >> +
> >> +	jz4740_dma_set_complete_cb(chan->jz_chan, jz4740_dma_complete_cb);
> >> +
> >> +	return 0;
> > Zero is not expected value, you need to return the descriptors allocated
> > sucessfully.
> 
> Well, zero descriptors have been allocated. As far as I can see only a negative
> return value is treated as an error. Also the core doesn't seem to use the
> return value for anything else but checking if it is an error.
This is the API defination
* @device_alloc_chan_resources: allocate resources and return the
*      number of allocated descriptors

> >> +}
> >> +
> [...]
> >> +	dd->chancnt = 6;
> > hard coding is not advised
> 
> But there are 6 channels ;)
JZ4740_MAX_CH 6 :)

--
~Vinod
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