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sound/alsa: fix host hwparams calculation

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The host's period and buffer sizes were not being calculated correctly.

This resulted in timing mismatches.

This commit calculates the correct sizes by taking the guest's
parameters into account.

Impossible cases when matching with stream parameters will lead to
unreachable!().

Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
This commit is contained in:
Manos Pitsidianakis 2023-10-06 15:21:50 +03:00 committed by Alex Bennée
parent 84c58404b8
commit 2ba56bef25
1 changed files with 89 additions and 27 deletions
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116
staging/vhost-device-sound/src/audio_backends/alsa.rs
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@ -60,34 +60,37 @@ fn update_pcm(
match s.direction {
d if d == VIRTIO_SND_D_OUTPUT => Direction::Playback,
d if d == VIRTIO_SND_D_INPUT => Direction::Capture,
other => panic!("Invalid virtio-sound stream: {}", other),
// We initialize the stream direction ourselves in device.rs, so it should never
// have another value.
_ => unreachable!(),
},
false,
)?;
{
let rate = match s.params.rate {
virtio_sound::VIRTIO_SND_PCM_RATE_5512 => 5512,
virtio_sound::VIRTIO_SND_PCM_RATE_8000 => 8000,
virtio_sound::VIRTIO_SND_PCM_RATE_11025 => 11025,
virtio_sound::VIRTIO_SND_PCM_RATE_16000 => 16000,
virtio_sound::VIRTIO_SND_PCM_RATE_22050 => 22050,
virtio_sound::VIRTIO_SND_PCM_RATE_32000 => 32000,
virtio_sound::VIRTIO_SND_PCM_RATE_44100 => 44100,
virtio_sound::VIRTIO_SND_PCM_RATE_48000 => 48000,
virtio_sound::VIRTIO_SND_PCM_RATE_64000 => 64000,
virtio_sound::VIRTIO_SND_PCM_RATE_88200 => 88200,
virtio_sound::VIRTIO_SND_PCM_RATE_96000 => 96000,
virtio_sound::VIRTIO_SND_PCM_RATE_176400 => 176400,
virtio_sound::VIRTIO_SND_PCM_RATE_192000 => 192000,
virtio_sound::VIRTIO_SND_PCM_RATE_384000 => 384000,
// We check if a rate value is supported in PCM_SET_PARAMS so it should never have
// an unknown value.
_ => unreachable!(),
};
let hwp = HwParams::any(&pcm)?;
hwp.set_channels(s.params.channels.into())?;
hwp.set_rate(
match s.params.rate {
virtio_sound::VIRTIO_SND_PCM_RATE_5512 => 5512,
virtio_sound::VIRTIO_SND_PCM_RATE_8000 => 8000,
virtio_sound::VIRTIO_SND_PCM_RATE_11025 => 11025,
virtio_sound::VIRTIO_SND_PCM_RATE_16000 => 16000,
virtio_sound::VIRTIO_SND_PCM_RATE_22050 => 22050,
virtio_sound::VIRTIO_SND_PCM_RATE_32000 => 32000,
virtio_sound::VIRTIO_SND_PCM_RATE_44100 => 44100,
virtio_sound::VIRTIO_SND_PCM_RATE_48000 => 48000,
virtio_sound::VIRTIO_SND_PCM_RATE_64000 => 64000,
virtio_sound::VIRTIO_SND_PCM_RATE_88200 => 88200,
virtio_sound::VIRTIO_SND_PCM_RATE_96000 => 96000,
virtio_sound::VIRTIO_SND_PCM_RATE_176400 => 176400,
virtio_sound::VIRTIO_SND_PCM_RATE_192000 => 192000,
virtio_sound::VIRTIO_SND_PCM_RATE_384000 => 384000,
_ => 44100,
},
ValueOr::Nearest,
)?;
hwp.set_rate(rate, ValueOr::Nearest)?;
hwp.set_rate_resample(false)?;
hwp.set_format(match s.params.format {
virtio_sound::VIRTIO_SND_PCM_FMT_IMA_ADPCM => Format::ImaAdPCM,
virtio_sound::VIRTIO_SND_PCM_FMT_MU_LAW => Format::MuLaw,
@ -114,17 +117,76 @@ fn update_pcm(
virtio_sound::VIRTIO_SND_PCM_FMT_DSD_U16 => Format::DSDU16LE,
virtio_sound::VIRTIO_SND_PCM_FMT_DSD_U32 => Format::DSDU32LE,
virtio_sound::VIRTIO_SND_PCM_FMT_IEC958_SUBFRAME => Format::iec958_subframe(),
_ => Format::Unknown,
// We check if a format value is supported in PCM_SET_PARAMS so it should never have
// an unknown value.
_ => unreachable!(),
})?;
hwp.set_access(Access::RWInterleaved)?;
// > A period is the number of frames in between each hardware interrupt.
// - https://www.alsa-project.org/wiki/FramesPeriods
let frame_size = u32::from(s.params.channels)
* match s.params.format {
virtio_sound::VIRTIO_SND_PCM_FMT_A_LAW
| virtio_sound::VIRTIO_SND_PCM_FMT_S8
| virtio_sound::VIRTIO_SND_PCM_FMT_U8
| virtio_sound::VIRTIO_SND_PCM_FMT_DSD_U8
| virtio_sound::VIRTIO_SND_PCM_FMT_MU_LAW => 1,
virtio_sound::VIRTIO_SND_PCM_FMT_S16
| virtio_sound::VIRTIO_SND_PCM_FMT_U16
| virtio_sound::VIRTIO_SND_PCM_FMT_DSD_U16
| virtio_sound::VIRTIO_SND_PCM_FMT_IMA_ADPCM => 2,
virtio_sound::VIRTIO_SND_PCM_FMT_S18_3
| virtio_sound::VIRTIO_SND_PCM_FMT_U18_3
| virtio_sound::VIRTIO_SND_PCM_FMT_S20_3
| virtio_sound::VIRTIO_SND_PCM_FMT_U20_3
| virtio_sound::VIRTIO_SND_PCM_FMT_S24_3
| virtio_sound::VIRTIO_SND_PCM_FMT_U24_3
| virtio_sound::VIRTIO_SND_PCM_FMT_S24
| virtio_sound::VIRTIO_SND_PCM_FMT_U24 => 3,
virtio_sound::VIRTIO_SND_PCM_FMT_S20
| virtio_sound::VIRTIO_SND_PCM_FMT_U20
| virtio_sound::VIRTIO_SND_PCM_FMT_S32
| virtio_sound::VIRTIO_SND_PCM_FMT_U32
| virtio_sound::VIRTIO_SND_PCM_FMT_FLOAT
| virtio_sound::VIRTIO_SND_PCM_FMT_DSD_U32
| virtio_sound::VIRTIO_SND_PCM_FMT_IEC958_SUBFRAME => 4,
virtio_sound::VIRTIO_SND_PCM_FMT_FLOAT64 => 8,
// We check if a format value is supported in PCM_SET_PARAMS so it should never
// have an unknown value.
_ => unreachable!(),
};
// Calculate desirable bytes/sec rate to achieve the stream's desired
// parameters:
let bps_rate = frame_size * rate;
// Calculate period size for ~100ms (arbitrary) interrupt period:
let period_bytes = bps_rate / 10;
// Finally, calculate the size of a period (in frames):
let period_frames = period_bytes / frame_size;
hwp.set_period_size(period_frames as i64, alsa::ValueOr::Less)?;
// Online ALSA driver recommendations seem to be that the buffer should be at
// least 2 * period_size.
//
// FIXME: What values should we set for buffer size and period size? (Should we
// set them at all?) virtio-sound spec deals in bytes but ALSA deals
// in frames. The alsa bindings sometimes use frames and sometimes bytes.
// https://www.alsa-project.org/wiki/FramesPeriods says:
//
// > It seems (writing-an-alsa-driver.pdf), however, that it is the ALSA runtime that
// > decides on the actual buffer_size and period_size, depending on: the requested
// > number of channels, and their respective properties (rate and sampling resolution) -
// > as well as the parameters set in the snd_pcm_hardware structure (in the driver).
//
// So, if the operation fails let's assume the ALSA runtime has set a better value.
if let Err(err) = hwp.set_buffer_size_near(2 * period_frames as i64) {
log::error!("could not set buffer size {}: {}", 2 * period_frames, err);
}
// Read more at https://www.alsa-project.org/wiki/FramesPeriods.
pcm.hw_params(&hwp)?;
}