Bluetooth Audio Debugging

Solving call audio with bluetooth headset

After the switch from Kernel version 4.4(LA.UM.6.4.r1) to 4.9(LE.UM.2.3.2.r1.4), the Sony Xperia XZ(“kagura”) could not output any call sound at all while a bluetooth headset was connected.

While digging through the dmesg logs, some things popped up:

qdsp_cvp_callback: cmd = 0x13199 returned error = 0x2
voice_send_cvp_device_channels_cmd: DSP returned error[ADSP_EBADPARAM]
voice_send_cvp_media_fmt_info_cmd: Set channel info failed err: -22
voice_setup_vocproc: Set media format info failed err:-22
setup voice failed

The messages are emitted by q6voice.c. (The techpack/ directory contains backports/imports that are not in the regular kernel.)

Let’s add some logging to 4.9:

2019-01-29-1845-4.9-with-logging-dmesg10.txt
voc_set_device_config: path_dir=0 port_id=100a, channels=1, sample_rate=16000, \
  bits_per_sample=2
voice_send_cvp_create_cmd: veeeery_early: v->dev_rx.no_of_channels = 1
voice_send_cvp_create_cmd: veeeery_early: v->dev_tx.no_of_channels = 1
voice_set_topology_specific_info: Topology Rx no of channels: 15
voice_set_topology_specific_info: Topology Tx no of channels: 15
voice_send_cvp_create_cmd: early: v->dev_rx.no_of_channels = 15
voice_send_cvp_create_cmd: early: v->dev_tx.no_of_channels = 15
tx_topology: 69491 tx_port_id=4107, rx_port_id=4106, mode: 0x10f7c
rx_topology: 69514, profile_id: 0x1135e, pkt_size: 64
voice_send_cvp_create_cmd: late: v->dev_rx.no_of_channels = 15
voice_send_cvp_create_cmd: late: v->dev_tx.no_of_channels = 15
voice_send_cvp_device_channels_cmd: cvp_set_dev_channels_cmd struct follows:
voice_send_cvp_device_channels_cmd: hdr: hdr_field=592, pkt_size=24, src_port=6, \
  dest_port=64, token=0, opcode=78233
voice_send_cvp_device_channels_cmd: cvp_set_channels: \
  rx_num_channels=1, tx_num_channels=15
qdsp_cvp_callback: cmd = 0x13199 returned error = 0x2
voice_send_cvp_device_channels_cmd: DSP returned error[ADSP_EBADPARAM]
voice_send_cvp_media_fmt_info_cmd: Set channel info failed err: -22
voice_setup_vocproc: Set media format info failed err:-22
setup voice failed

…and compare with 4.4:

2019-01-29-1845-4.4-with-logging-dmesg.txt
voice_send_cvp_device_channels_cmd: cvp_set_dev_channels_cmd struct follows:
voice_send_cvp_device_channels_cmd: hdr: hdr_field=592, pkt_size=24, src_port=6, \
  dest_port=64, token=0, opcode=78233
voice_send_cvp_device_channels_cmd: cvp_set_channels: \
  rx_num_channels=1, tx_num_channels=1

We can immediately see something is odd with rx_num_channels and tx_num_channels.

Hardcoding tx_num_channels to 1 seems to temporarily solve the issue, we have call audio again.

But that’s not a good solution, let’s dig a bit deeper:
The number of channels is frozen on 4.4, but starting on 4.9 the kernel loads voice topology information via voc_get_tx_rx_topology() - including the number of channels - from the ACDB(“Audio Calibration Database”). ACDB is a proprietary mechanism, and we cannot modify the binary acdb files without specialized tools.

It seems the calibration data, at least in respect to bluetooth voice channels, is off for legacy “tone” devices such as the Xperia XZ(“kagura”), and possibly “loire” too.

So we arrive at the next idea: Only read topology on nile, tama and newer platforms(where the ACDB is correct) via of_machine_is_compatible: Do not load bt audio topology on legacy devices.

But that’s also not a very good idea since we are now nuking all ACDB topology info in q6voice for legacy when only bluetooth seems wrongly configured.

The final decision was to do it more elegantly: Just disable the acdb_id for OUT_BT_SCO_WB in the legacy platforms’ audio_platform_info.xml files.

See:

But there is still some way to go, when switching from bluetooth to earpiece/speaker the sound is gone irrevocably, one needs to restart call to restore it. It seems the issue is completely gone with the v6 Software Binaries realease.

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