feat(alsa): enumerate up to 64 channels (AES10 maximum)

Author: roderickvd

CHANGELOG.md

@@ -88,6 +88,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **ALSA**: Streams no longer start automatically on creation; call `play()` manually.
 - **ALSA**: The `realtime` feature now skips RT promotion for ineligible PCM types (null,
   I/O plugins, wrapper types); `audio_thread_priority` promoted unconditionally.
+- **ALSA**: Supported configurations are now enumerated up to 64 channels (AES10 maximum).
 - **ASIO**: `Device::driver`, `asio_streams`, and `current_callback_flag` are no longer `pub`.
 - **ASIO**: Timestamps now include driver-reported hardware latency.
 - **ASIO**: Hardware latency is now re-queried when the driver reports `kAsioLatenciesChanged`.

src/host/alsa/mod.rs

@@ -516,7 +516,11 @@ impl Device {
         };
 
         let min_channels = hw_params.get_channels_min()?;
-        let max_channels = hw_params.get_channels_max()?.min(32); // TODO: cap at 32 or too many configs
+        // 64 = AES10 (MADI) maximum; also prevents spinning on plugins like plughw that report u32::MAX.
+        const CHANNEL_ENUM_CAP: u32 = 64;
+        let max_channels = hw_params
+            .get_channels_max()?
+            .min(min_channels.max(CHANNEL_ENUM_CAP));
 
         let mut output = Vec::new();
         let mut seen_formats: Vec<SampleFormat> = Vec::new();
@@ -1685,7 +1689,8 @@ impl From<alsa::Error> for Error {
             libc::ENODEV | libc::ENOENT | LIBC_ENOTSUPP => ErrorKind::DeviceNotAvailable.into(),
             libc::EPERM | libc::EACCES => ErrorKind::PermissionDenied.into(),
             libc::EBUSY | libc::EAGAIN => ErrorKind::DeviceBusy.into(),
-            libc::EINVAL | libc::ENOSYS => ErrorKind::UnsupportedConfig.into(),
+            libc::EINVAL => ErrorKind::UnsupportedConfig.into(),
+            libc::ENOSYS => ErrorKind::UnsupportedOperation.into(),
             libc::EPIPE => ErrorKind::Xrun.into(),
             _ => Error::with_message(ErrorKind::BackendError, err.to_string()),
         }