Regression playing 24bit/96kHz audio on USB audio interface between 5.10.94 and 5.15.21

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Hi,

I have a program that configures a Behringer UMC404HD 192k USB audio interface for playback as follows (pseudocode):

  snd_pcm_hw_params_set_channels(pcm, hwp, 2);
  snd_pcm_hw_params_set_format(pcm, hwp, SND_PCM_FORMAT_S24_3LE);
  snd_pcm_hw_params_set_access(pcm, hwp, SND_PCM_ACCESS_MMAP_INTERLEAVED);
  snd_pcm_hw_params_set_rate(pcm, hwp, val=96000, dir=0);
  snd_pcm_hw_params_set_period_size_near(pcm, hwp, val=513, dir=0);
  // If I confirm at this point with snd_pcm_hw_params_get_period_size,
  // I get back 513.
  snd_pcm_hw_params_set_buffer_size_near(pcm, hwp, val=2052);
  snd_pcm_hw_params(pcm, hwp);
  // If I confirm with snd_pcm_hw_params_get_buffer_size,
  // I get back 2052.

On Linux 5.10.94 (specifically Arch Linux ARM package linux-rpi-5.10.94-1), this succeeds, and I can play back audio just fine. On 5.15.21 (specifically linux-rpi-5.15.21-3), all the calls succeed apart from the last one, which returns EINVAL.

(My actual program is written in Rust and uses a Rust wrapper library for libasound, https://docs.rs/alsa/0.6.0/alsa/, but the calls should be the ones listed.)

I confirmed with snd_pcm_hw_params_test_format that the S24_3LE format is supported. On both kernels it is successful. I confirmed with snd_pcm_hw_params_test_rate that 96 kHz is supported. On both kernels it is successful. There are differences though. When I query these:

  snd_pcm_hw_params_get_period_size_min
  snd_pcm_hw_params_get_period_size_max
  snd_pcm_hw_params_get_buffer_size_min
  snd_pcm_hw_params_get_buffer_size_max

Then on 5.10.94 (the good version), I get:

  period size min/max: 12/32768, buffer size min/max: 24/65536

But on 5.15.21 (the bad version), I get:

  period size min/max: 13/71332, buffer size min/max: 26/142663

Also, after I set the period size to 513, if I then query the buffer size min/max, on 5.10.94 I get:

  buffer size min/max: 1026/65536

But on 5.15.21 I get:

  buffer size min/max: 1027/142663

In lsmod, snd_usb_audio shows up, and from lsusb -v, the UMC404HD appears to be a standard USB audio interface. The lsusb output is identical on both kernels.

Please let me know if there is anything I can do to help further diagnose the issue, or if I should report this elsewhere.

Kind regards,
Ruud van Asseldonk



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