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

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Date:	Fri, 24 May 2013 08:41:05 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Vinod Koul <vinod.koul@...el.com>
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 05/24/2013 07:54 AM, Vinod Koul wrote:
> 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..

I do copy the full config, not just the pointer to the config. Although
src_addr and dest_addr are the only two fields which are used later on at this
point. So I could change it to just copy src_addr and dest_addr, or well just
one of them depending on the direction.

> 
>>
>>>> +}
>> [...]
>>>> +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
> 

But 0 is still the number of descriptors that have been pre-allocated.

- Lars


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