[alsa-devel] [alsa-utils] [PATCH] Add support for no-rewind flag in aplay utility

[Takashi Sakamoto]

Hi,

On Jan 31 2018 09:14, Pierre-Louis Bossart wrote:
> On 1/30/18 11:40 AM, Takashi Sakamoto wrote:
>> Hi,
>>
>> On Jan 30 2018 18:34, Sriram Periyasamy wrote:
>>> From: Ramesh Babu <ramesh.babu at intel.com>
>>>
>>> The "no-rewind" flag is introduced in alsa.
>>> Application can use this flag to assure kernel driver
>>> that rewind won't be exercised. Driver could use this
>>> flag to alter it's buffering scheme to optimize power
>>> and performance.
>>>
>>> Signed-off-by: Ramesh Babu <ramesh.babu at intel.com>
>>> Signed-off-by: Sriram Periyasamy <sriramx.periyasamy at intel.com>
>>> ---
>>>   aplay/aplay.c | 14 +++++++++++++-
>>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> Current implementation of 'aplay' doesn't perform rewinding/forwarding,
>> thus an additional of this option is surplus.
> 
> It helps tell the driver that rewinds won't be used and indirectly that 
> the appl_ptr updates are passed to the hardware.
> Removing the option or making the functionality unconditional removes 
> the freedom to test with or without this option.
 From name of this option, I understand that your intension is to set
hardware parameter with your new flag 'SND_PCM_HW_PARAMS_NO_REWINDS' so
that ALSA PCM core doesn't allow applications to perform
rewinding/forwarding requests because your drivers for Intel ATOM
platform with SSP (without HDA) and DSP core and specific firmwares
including blobs for ALSA topology interface are not allowed to
invalidate queued PCM frames in buffer dedicated to DMA transmission due
to restrictions of the hardware.

However, aplay is _not_ written to perform the rewinding/forwarding
requests, thus we never check actual effects of the flag because it
never kick your driver for the invalidation. Your new option for aplay
has no practical meaning for running PCM runtime.

I oppose an addition of this flag to keep this basic utility readable,
understandable and being small for easy maintainance. At least, I'd not
like to explain about an aim of this makeshift option every time to be
asked by developers and users, instead of you.

>>> diff --git a/aplay/aplay.c b/aplay/aplay.c
>>> index 6b740c281f8e..b50602a59024 100644
>>> --- a/aplay/aplay.c
>>> +++ b/aplay/aplay.c
>>> @@ -108,6 +108,7 @@ static snd_pcm_stream_t stream = 
>>> SND_PCM_STREAM_PLAYBACK;
>>>   static int mmap_flag = 0;
>>>   static int interleaved = 1;
>>>   static int nonblock = 0;
>>> +static int no_rewind = 0;
>>>   static volatile sig_atomic_t in_aborting = 0;
>>>   static u_char *audiobuf = NULL;
>>>   static snd_pcm_uframes_t chunk_size = 0;
>>> @@ -229,6 +230,7 @@ _("Usage: %s [OPTION]... [FILE]...\n"
>>>   "-I, --separate-channels one file for each channel\n"
>>>   "-i, --interactive       allow interactive operation from stdin\n"
>>>   "-m, --chmap=ch1,ch2,..  Give the channel map to override or follow\n"
>>> +"-w, --no-rewind         enables no rewind mode\n"
>>>   "    --disable-resample  disable automatic rate resample\n"
>>>   "    --disable-channels  disable automatic channel conversions\n"
>>>   "    --disable-format    disable automatic format conversions\n"
>>> @@ -470,7 +472,7 @@ int main(int argc, char *argv[])
>>>   {
>>>       int duration_or_sample = 0;
>>>       int option_index;
>>> -    static const char short_options[] = 
>>> "hnlLD:qt:c:f:r:d:s:MNF:A:R:T:B:vV:IPCi"
>>> +    static const char short_options[] = 
>>> "hnlLD:qt:c:f:r:d:s:w:MNF:A:R:T:B:vV:IPCi"
>>>   #ifdef CONFIG_SUPPORT_CHMAP
>>>           "m:"
>>>   #endif
>>> @@ -514,6 +516,7 @@ int main(int argc, char *argv[])
>>>           {"process-id-file", 1, 0, OPT_PROCESS_ID_FILE},
>>>           {"use-strftime", 0, 0, OPT_USE_STRFTIME},
>>>           {"interactive", 0, 0, 'i'},
>>> +        {"no-rewind", 0, 0, 'w'},
>>>           {"dump-hw-params", 0, 0, OPT_DUMP_HWPARAMS},
>>>           {"fatal-errors", 0, 0, OPT_FATAL_ERRORS},
>>>   #ifdef CONFIG_SUPPORT_CHMAP
>>> @@ -753,6 +756,9 @@ int main(int argc, char *argv[])
>>>           case 'i':
>>>               interactive = 1;
>>>               break;
>>> +        case 'w':
>>> +            no_rewind = 1;
>>> +            break;
>>>           case OPT_DISABLE_RESAMPLE:
>>>               open_mode |= SND_PCM_NO_AUTO_RESAMPLE;
>>>               break;
>>> @@ -1396,6 +1402,12 @@ static void set_params(void)
>>>                                    &buffer_frames);
>>>       }
>>>       assert(err >= 0);
>>> +
>>> +    if (no_rewind) {
>>> +        err = snd_pcm_hw_params_set_no_rewind(handle, params, 1);
>>> +        assert(err >= 0);
>>> +    }
>>> +
>>>       monotonic = snd_pcm_hw_params_is_monotonic(params);
>>>       can_pause = snd_pcm_hw_params_can_pause(params);
>>>       err = snd_pcm_hw_params(handle, params);


Takashi Sakamoto