[BUG] Internal microphone not working on Xiaomi Book Pro 14 (TM2424) - PTL + RT721

[aachen0]

[BUG] Internal microphone not working on Xiaomi Book Pro 14 (TM2424) - PTL + RT721

System Information

• Laptop: Xiaomi Book Pro 14 (TM2424)
• BIOS Version: XMAPT4B0P0A0A
• OS: Kylin Linux Desktop V10 SP1 (based on Ubuntu 20.04)
• Kernels Tested: 7.1.3-070103-generic (Kylin), 7.1.5-070105-generic (Ubuntu mainline), 6.12.95-061295-generic
• Audio Controller: Intel PTL (Panther Lake), PCI 0000:00:1f.3
• Codec: Realtek RT721 (SoundWire, mfg_id 0x025d, part_id 0x0721) + RT1320 amplifier
• Internal microphone: Confirmed working under Windows 11 on the same hardware

Issue Description

The built-in microphone produces no audio on Linux. Recording yields all-zero samples. The UKUI sound settings panel shows "No input device" (输入设备：无). Audio playback (speakers) works correctly.

Kernel Log Analysis

During boot, the SOF driver reports:

sof-audio-pci-intel-ptl 0000:00:1f.3: No SoundWire machine driver found for the ACPI-reported configuration:
sof-audio-pci-intel-ptl 0000:00:1f.3: link 3 mfg_id 0x025d part_id 0x0721 version 0x3
sof-audio-pci-intel-ptl 0000:00:1f.3: link 3 mfg_id 0x025d part_id 0x1320 version 0x3
sof-audio-pci-intel-ptl 0000:00:1f.3: Use SoundWire default machine driver with function topologies
sof-audio-pci-intel-ptl 0000:00:1f.3: DMICs detected in NHLT tables: 0

The SDCA functions are detected by ACPI:

acpi device:1f: SDCA function UAJ (type 6) at 0x1
acpi device:20: SDCA function SmartMic (type 3) at 0x2
acpi device:21: SDCA function HID (type 10) at 0x3
acpi device:23: SDCA function SmartAmp (type 1) at 0x4

The function topologies are loaded:

loading topology 0: intel/sof-ipc4-tplg/sof-sdca-jack-id0.tplg
loading topology 1: intel/sof-ipc4-tplg/sof-sdca-mic-id4.tplg
loading topology 2: intel/sof-ipc4-tplg/sof-sdca-1amp-id2.tplg
loading topology 3: intel/sof-ipc4-tplg/sof-hdmi-pcm5-id5.tplg

However, the PulseAudio card profiles remain output-only (no input profiles):

Profiles:
    output:stereo-fallback: 立体声 输出 (sinks: 1, sources: 0, priority: 37868, available: no)
    output:multichannel-output: 多声道 输出 (sinks: 1, sources: 0, priority: 32868, available: no)
    off: 关 (sinks: 0, sources: 0, priority: 0, available: no)

ALSA Capture Path

The ALSA layer shows capture devices exist:

• hw:0,1 - Jack In (headset microphone)
• hw:0,4 - Microphone (internal)
• hw:0,10 - DMIC Raw (created when dmic_num=2 is set)

The RT721 mixer controls show the capture path is configured:

• rt721 ADC 09 Mux = MIC2 (analog microphone input selected)
• rt721 FU0F Capture Switch = on,on
• rt721 FU0F Capture Volume = 63,63 (maximum)
• rt721 FU1E Capture Switch = on,on,on,on
• rt721 FU1E Capture Volume = 63,63,63,63 (maximum)
• rt721 FU15 Boost Volume = 3,3,3,3 (maximum, +30dB)

Despite all capture settings at maximum, recording from any capture device produces only silence (all-zero samples).

What Was Tried

1. PulseAudio configuration: Set default source, adjusted volumes — no effect
2. ALSA mixer tuning: Set all capture switches to on, volumes to maximum, boost to maximum — no effect
3. Module parameter snd_soc_sof_sdw.quirk=0x40 (SOC_SDW_PCH_DMIC) — no effect
4. Module parameter snd_sof_intel_hda_generic dmic_num=2: Creates DMIC Raw device (hw:0,10) but still produces silence
5. Module parameter tplg_filename=sof-ptl-rt721.tplg: Broke speaker output entirely
6. Kernel 6.12.95-061295: No sound card detected at all (complete regression)
7. Kernel 7.1.5-070105: Same microphone issue persists
8. PipeWire: Not available in Kylin repos

Root Cause Analysis

The core issue appears to be:

1. NHLT tables report 0 DMICs despite the laptop having a built-in microphone that works under Windows
2. No matching SoundWire machine driver is found for this Xiaomi laptop's ACPI configuration
3. Function topologies are used instead of device-specific topologies, and the resulting card profiles lack input support
4. The microphone may be wired to the RT721's analog MIC2 input rather than a PCH DMIC path, but the topology/machine driver configuration doesn't properly enable this capture path

Related Issues

• #5053 - Xiaomi Redmibook 16 2024 mic not working (closed as duplicate)
• #5860 - Xiaomi RedmiBook 16 2025 mic not working (AMD)
• #5817 - SOF fails to load DSP topology for PTL (closed)
• PR #5739 - RT712/RT721 CODEC_MIC quirk fix (merged May 2026)

Request

1. Is there a DMI match or ACPI override needed for this Xiaomi laptop model (TM2424)?
2. Is there a specific BIOS configuration or update required to properly report DMIC in NHLT tables?
3. Are there any additional patches or configuration parameters needed for RT721 microphone support on PTL platforms?

I am happy to provide any additional debug information (full dmesg, ALSA dump, ACPI table dump, etc.) as needed.