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

[Ruud van Asseldonk]

Hi all,

This issue is still present in 5.15.82, is there anything I can do to 
diagnose this further?

Best,

Ruud van Asseldonk

> 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