Re: [alsa-devel] [PATCH 3/6] dma: Add a jz4740 dmaengine driver

[Lars-Peter Clausen <lars@metafoo.de>]

>>>>>> +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.
> and that should change, typically the driver will preallocate a pool of
> descriptors. These are to be used later for .device_prep_xxx calls.
> 

Since the size of the descriptor is not know in advance this is not possible.

- Lars