[alsa-devel] snd_pcm_set_params faild on set_buffer_time_near and set_period_time_near

[Martin Geier]

Thanks for help,

in attachment is patch with suggest change.
Is the patch acceptable?

Martin

On 23.07.2015 10:11, Takashi Iwai wrote:
> On Tue, 21 Jul 2015 10:52:01 +0200,
> Martin Geier wrote:
>> Hallo,
>>
>> I tried to configure alsa device with snd_pcm_set_params function,
>> requested
>> parameters was:
>> channel 2, rate: 22050, soft_resample: 1, latency: 50000
>>
>> Function snd_pcm_hw_params_set_buffer_time_near and
>> snd_pcm_hw_param_set_near
>> is called with:
>> min: 50000, max: 50000, mindir: 0, maxdir: -1
>>
>> and input params was:
>>
>> ACCESS:  RW_INTERLEAVED
>> FORMAT:  S16_LE
>> SUBFORMAT:  STD
>> SAMPLE_BITS: 16
>> FRAME_BITS: 32
>> CHANNELS: 2
>> RATE: 22050
>> PERIOD_TIME: (362 743039)
>> PERIOD_SIZE: [8 16384]
>> PERIOD_BYTES: [32 65536]
>> PERIODS: [2 19]
>> BUFFER_TIME: (725 1486078)
>> BUFFER_SIZE: [16 32768]
>> BUFFER_BYTES: [64 131072]
>> TICK_TIME: ALL
>>
>> unfortunately, this function fails, on function snd_pcm_hw_param_set_first:
>>
>> ALSA ERROR hw_params: set_near (BUFFER_TIME)
>>              value = 50000 : Invalid argument
>> ACCESS:  RW_INTERLEAVED
>> FORMAT:  S16_LE
>> SUBFORMAT:  STD
>> SAMPLE_BITS: 16
>> FRAME_BITS: 32
>> CHANNELS: 2
>> RATE: 22050
>> PERIOD_TIME: (4580 5533)
>> PERIOD_SIZE: NONE
>> PERIOD_BYTES: [404 488]
>> PERIODS: 10
>> BUFFER_TIME: (50022 50023)
>> BUFFER_SIZE: 1103
>> BUFFER_BYTES: 4412
>> TICK_TIME: ALL
>>
>> This shouldn't be problem because in snd_pcm_set_params is
>> snd_pcm_hw_params_set_period_time_near called.
>> This function should be called with same params as
>> snd_pcm_hw_params_set_buffer_time_near
>> but the input params are:
>>
>> snd_pcm_hw_param_set_near: min: 12500, max: 12500, mindir: 0, maxdir: -1
>> hw_params: snd_pcm_hw_param_set_near (PERIOD_TIME)
>> ACCESS:  RW_INTERLEAVED
>> FORMAT:  S16_LE
>> SUBFORMAT:  STD
>> SAMPLE_BITS: 16
>> FRAME_BITS: 32
>> CHANNELS: 2
>> RATE: 22050
>> PERIOD_TIME: (4580 5533)
>> PERIOD_SIZE: NONE
>> PERIOD_BYTES: [404 488]
>> PERIODS: 10
>> BUFFER_TIME: (50022 50023)
>> BUFFER_SIZE: 1103
>> BUFFER_BYTES: 4412
>> TICK_TIME: ALL
>>
>> because in snd_pcm_hw_param_set_near is
>>
>> if (last)
>>       err = snd_pcm_hw_param_set_last(pcm, params, var, val, dir);
>> else
>>       err = snd_pcm_hw_param_set_first(pcm, params, var, val, dir);
>> if (err < 0)
>>       dump_hw_params(params, "set_near", var, *val, err);
>> return err;
>>
>> and in error part is only debug output and not restore original parameters.
>>
>> Environment:
>> alsa-lib 1.0.27.1
>> TI AM335x soc
>>
>> Simple fix is attached, but I am not sure if it is correct.
> Thanks for analysis and patch.  It's however rather a bug in
> snd_pcm_set_params().  There is no guarantee to keep the old value in
> snd_pcm_set_*(), thus the caller needs to take care of it instead.
>
>
> Takashi
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