[RFC PATCH 1/1] ASoC: soc-core: symmetry checking for each DAIs separately

[lars@metafoo.de (Lars-Peter Clausen)]

On 08/26/2011 03:57 PM, Dong Aisheng-B29396 wrote:
>> -----Original Message-----
>> From: Lars-Peter Clausen [mailto:lars at metafoo.de]
>> Sent: Friday, August 26, 2011 9:33 PM
>> To: Dong Aisheng-B29396
>> Cc: alsa-devel at alsa-project.org; linux-arm-kernel at lists.infradead.org;
>> broonie at opensource.wolfsonmicro.com; lrg at ti.com; s.hauer at pengutronix.de;
>> w.sang at pengutronix.de
>> Subject: Re: [RFC PATCH 1/1] ASoC: soc-core: symmetry checking for each
>> DAIs separately
>>
>> On 08/26/2011 03:17 PM, Dong Aisheng-B29396 wrote:
>>>> -----Original Message-----
>>>> From: Lars-Peter Clausen [mailto:lars at metafoo.de]
>>>> Sent: Friday, August 26, 2011 7:24 PM
>>>> To: Dong Aisheng-B29396
>>>> Cc: alsa-devel at alsa-project.org;
>>>> linux-arm-kernel at lists.infradead.org;
>>>> broonie at opensource.wolfsonmicro.com; lrg at ti.com;
>>>> s.hauer at pengutronix.de; w.sang at pengutronix.de
>>>> Subject: Re: [RFC PATCH 1/1] ASoC: soc-core: symmetry checking for
>>>> each DAIs separately
>>>>
>>>> On 08/26/2011 11:35 AM, Dong Aisheng wrote:
>>>>> [...]
>>>>>  	/* runtime devices */
>>>>> diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c index
>>>>> 1aee9fc..3f7ded7 100644
>>>>> --- a/sound/soc/soc-pcm.c
>>>>> +++ b/sound/soc/soc-pcm.c
>>>>> @@ -32,33 +32,54 @@ static int soc_pcm_apply_symmetry(struct
>>>> snd_pcm_substream *substream)
>>>>>  	struct snd_soc_pcm_runtime *rtd = substream->private_data;
>>>>>  	struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
>>>>>  	struct snd_soc_dai *codec_dai = rtd->codec_dai;
>>>>> +	unsigned int race;
>>>>> +	unsigned int force_rate;
>>>>>  	int ret;
>>>>>
>>>>> +	race = 0;
>>>>> +	force_rate = 0;
>>>>> +
>>>>>  	if (!codec_dai->driver->symmetric_rates &&
>>>>>  	    !cpu_dai->driver->symmetric_rates &&
>>>>>  	    !rtd->dai_link->symmetric_rates)
>>>>>  		return 0;
>>>>>
>>>>> +	if (codec_dai->active && codec_dai->driver->symmetric_rates ||
>>>>> +	     codec_dai->active && rtd->dai_link->symmetric_rates) {
>>>>
>>>> parenthesis, please, when mixing && and || in the same expression.
>>>> Makes it easier to comprehend and protects against accidental mistakes.
>>> Thanks for reminder, I will take it.
>>>
>>>>> +		if (codec_dai->rate != 0)
>>>>> +			force_rate = codec_dai->rate;
>>>>> +		else
>>>>> +			race = 1;
>>>>> +	}
>>>>> +
>>>>> +	if (cpu_dai->active && cpu_dai->driver->symmetric_rates ||
>>>>> +	    codec_dai->active && rtd->dai_link->symmetric_rates) {
>>>>> +		if (cpu_dai->rate != 0)
>>>>> +			force_rate = cpu_dai->rate;
>>>>> +		else
>>>>> +			race = 1;
>>>>> +	}
>>>>> +
>>>>
>>>> If both dais are active and require symmetry we should call
>>>> snd_pcm_hw_constraint_minmax for both rates. This will ensure that if
>>>> both are already active and are running at different rates that there
>>>> will be no valid rate for the new pcm stream. Maybe extend this
>>>> function to take the dai as an parameter and call it twice, once for
>>>> the codec_dai and once for the cpu_dai.
>>>> This would allow to keep the current structure of the function.
>>> I was doing like the way as you said before, however, I found the
>>> question is that do we have to call snd_pcm_hw_constraint_minmax for
>>> the same substream two times?
>>>
>>> I just thought they should be running at the same rate if both are
>> active.
>>> Can you help point out in which case they may be different?
>>>
>>
>> This might be some rather obscure and theoretical setup but image the
>> following
>> situation:
>>
>> A   C
>>  \ / \
>>   B   D
>>
>> The link between A and B and the link between C and D are active and
>> running at different rates. Activating the link between C and B should
>> fail, since both are already active and are running at different rates.
>>
> Yes, it's a theoretical case.
> If we add the checking as below:
> If (cpu_dai->active && codec_dai->active
>     && cpu_dai->rate != codec_dai->rate)
> 	dev_err(...);
> I guess this may not work since that it's possible when DAI is active while
> it's rate is still not set.
> 
> Taking account of this case may bring a bit more complexity.
> Do you have any other suggestion? 
> Can we prevent it happen in machine layer?

Actually I think it will reduce code complexity, since it allows us to apply
the rate constraint for each dai independent of the other. And there should be
no harm in calling snd_pcm_hw_constraint_minmax twice with the same rate.

Just add a second parameter to soc_pcm_apply_symmetry taking a dai and call it
for each dai like.

	if (cpu_dai->active) {
		ret = soc_pcm_apply_symmetry(substream, cpu_dai);
		if (ret != 0)
			goto config_err;
	}
	if (codec_dai->active) {
		ret = soc_pcm_apply_symmetry(substream, codec_dai);
		if (ret != 0)
			goto config_err;
	}

The downside of this might be though that we can get the race warning twice.