[alsa-devel] alsalib and snd_pcm_hw_params_set_rate_minmax

[Oleksandr Andrushchenko]

+Konrad

On 03/15/2018 10:29 PM, Takashi Iwai wrote:
> On Thu, 15 Mar 2018 14:39:33 +0100,
> Oleksandr Andrushchenko wrote:
>> On 03/15/2018 03:23 PM, Takashi Iwai wrote:
>>> On Thu, 15 Mar 2018 13:20:14 +0100,
>>> Oleksandr Andrushchenko wrote:
>>>> On 03/15/2018 01:59 PM, Takashi Sakamoto wrote:
>>>>> Hi,
>>>>>
>>>>> On Mar 15 2018 19:45, Oleksandr Andrushchenko wrote:
>>>>>> Is it possible for user-space to reduce configuration space
>>>>>> with snd_pcm_hw_params_set_rate_minmax and then change it
>>>>>> with another snd_pcm_hw_params_set_rate_minmax with values
>>>>>> out of the reduced config?
>>>>>>
>>>>>> For example, the initial min/max is 44100/48000 and I set 44100
>>>>>> first, e.g.
>>>>>>
>>>>>> snd_pcm_hw_params_set_rate_minmax(handle, hw_params, 44100, 0, 44100, 0)
>>>>>>
>>>>>> and then want
>>>>>>
>>>>>> snd_pcm_hw_params_set_rate_minmax(handle, hw_params, 48000, 0, 48000, 0)
>>>>>>
>>>>>> Obviously, the last call fails as we have already a reduced
>>>>>> space of [44100; 44100].
>>>>>>
>>>>>> Is there a way I can still set the range to [48000; 48000]?
>>>>>>
>>>>>> Thank you,
>>>>>> Oleksandr
>>>>>>
>>>>>> P.S. This is in context of work done for [1]
>>>>>>
>>>>>> [1] https://www.spinics.net/lists/alsa-devel/msg75382.html
>>>>> We can't. Once shrinking available interval of a parameter, we cannot
>>>>> expand it again without initializing the parameter on memory object for
>>>>> 'struct snd_pcm_hw_params_t', in which actual layout is never disclosed
>>>>> to user applications.
>>>> So, this effectively means that this is a one way road, if you need to
>>>> change
>>>> some parameter you'll need to start all over, so the whole configuration
>>>> space remains consistent :(
>>> Yes, that's the design.  The only way to expand is to reset the whole,
>>> space and reduce again to the given size.
>>>
>> Clear, thank you
>>>>> If you can initialize whole the parameters, snd_pcm_hw_params_any() is
>>>>> available for your purpose, then set min/max rate again.
>>>> This is what I do now but...
>>>>> But just for
>>>>> one of the parameters, in my opinion, we need to open an internal
>>>>> API; snd_pcm_hw_param_any()[1].
>>>> IMO, this will lead to the false assumption that configuration is possible.
>>>> For example, I set 4 channels and 44100, but then, after
>>>> snd_pcm_hw_params_any,
>>>> set 48000 and might assume that the configuration is still
>>>> possible. But this may not
>>>> be true: it is true for the configuration returned by snd_pcm_hw_param_any
>>>> as we don't know about 4 channels yet. But might not be allowed if we
>>>> want 4 channels
>>>> and 48000 at the same time.
>>> Right.  At the point where snd_pcm_hw_params_any() is called, the
>>> whole configuration gets reset.  That's the reason I thought we may
>>> need to pass all 5 parameters in the query protocol.
>> Yes, I now start thinking of the same, e.g. if we pass
>> all 5 parameters (mask for formats and intervals for rate, channels,
>> buffer and period), then on backend side I can do something like:
>>
>> 1. snd_pcm_hw_params_any
>> 2. snd_pcm_hw_params_set_format_mask
>> 3. snd_pcm_hw_params_set_rate_minmax
>> 4. snd_pcm_hw_params_set_channels_minmax
>> 5. snd_pcm_hw_params_set_buffer_size_minmax
>> 6. snd_pcm_hw_params_set_period_size_minmax
>>
>> So, when finished the above confirms that configuration is possible.
>> The only concern here is that so many calls on backend side
>> might introduce start-up latency on frontend side though
>>
>>> IOW, the query stuff won't be modal, it just tries to reduce the given
>>> configuration space to the acceptable ranges.
>> Do you think the above solution with 5 parameters and the
>> corresponding snd_pcm_hw_params_set_xxx calls will do?
> I guess so, but let's model & test :)
I did some testing:
- frontend driver [1]
- sndif protocol [2]
- backend changes [3]

All seem to work now when I pass all 5 parameters while querying.
The only scary thing is that I had to change the size of
requests/responses in the sndif protocol from 32 to 64 bytes :(

Takashi, could you please have a quick look and tell me if
this is what you expect?
>
> thanks,
>
> Takashi
Thank you,
Oleksandr

[1] 
https://github.com/andr2000/linux/commits/tiwai_sound_for_next_pv_snd_upstream_v2
[2] https://github.com/andr2000/xen/commits/pr_sndif_v3
[3] https://github.com/andr2000/snd_be/commits/pr_hw_param