BUG] ASoC: amd: acp: NAU8821 I2S speaker machine missing on LG gram 16UD55U-GX5JK (ACP 7.0) — same p attern as ASUS PX13 fix in 7.0-rc6

Hi,

On an LG gram 16UD55U-GX5JK (AMD ACP 7.0, NAU8821 codec) running Ubuntu
26.04 LTS with kernel 7.0.0-15-generic, internal speakers are not exposed
as a playback PCM. The DMIC capture path on the same ACP block works.
This looks like the same class of problem recently fixed for ASUS ProArt
PX13 (HN7306EA) on ACP70 — platform ACPI/DMI not selecting the correct
machine driver, so only the PDM (mic) path comes up.

Reference fixes (Linux 7.0-rc6, sound pull):
   d0426510a9e1 - ASoC: amd: bypass faulty ACP ACPI config (ASUS PX13)
   399b6fd37a10 - ASoC: amd: acp: ACP70 SoundWire machine entry (ASUS PX13)
   2594196f4e3b - ASoC: amd: DMI quirk for ASUS HN7306EA ACP DMIC

My machine still has no LG gram / 16UD55U entry in the ACP machine or
NAU8821 quirk tables (no prior reports found on lore.kernel.org or
git.kernel.org for "16UD55U" / "16U55U").

Hardware
--------
- DMI (dmidecode): LG Electronics, Product 16UD55U-GX5JK, Board 16U55U
- DMI product string (from /proc/asound/card1 id):
   LGElectronics-16UD55U_GX5JK-Type1Version-16U55U
- AMD Audio Coprocessor PCI 0000:04:00.5 [1022:15e2] rev 72 (ACP 7.0)
- Radeon HDMI Audio 0000:04:00.1 [1002:1640] — playback OK (HDMI only)

Software
--------
- Ubuntu 26.04 LTS (resolute), kernel 7.0.0-15-generic
- linux-firmware 20260319, firmware-sof-signed 2025.12.2-1
- ACP70/SoundWire infrastructure present (snd_sof_amd_acp70,
   soundwire_amd, snd_amd_sdw_acpi loaded)

Symptom
-------
$ aplay -l
aplay: device_list:279: no soundcards found...

$ cat /proc/asound/cards
  0 [Generic        ]: HDA-Intel - HD-Audio Generic   (HDMI outputs only)
  1 [acppdmmach     ]: acp-pdm-mach - acp-pdm-mach
LGElectronics-16UD55U_GX5JK-Type1Version-16U55U

card1 has pcm0c (capture) only — no playback PCM for internal speakers.

Sysfs under 0000:04:00.5/acp_asoc_acp70.0/:
   acp-pdm-mach/   (registered)
   dmic-codec/
   (no I2S / NAU8821 speaker machine child)

Loaded modules (relevant):
   snd_acp_pci, snd_amd_acpi_mach, snd_acp_mach, snd_acp_legacy_mach,
   snd_soc_nau8821 (used by snd_acp_mach), snd_acp70, snd_acp_i2s,
   snd_acp_pdm, snd_acp_pcm

Firmware:
   /lib/firmware/amd/sof/ and amd/sof-tplg/ do not exist on Ubuntu;
   firmware-sof-signed only ships intel/sof-tplg/sof-acp.tplg for AMD.

Kernel log (excerpt):
   snd_acp_pci 0000:04:00.5: enabling device (0000 -> 0002)
(no nau8821 / acp-i2s machine probe messages)

Request
-------
Could you add a DMI quirk + ACP machine configuration for
LGElectronics-16UD55U_GX5JK (NAU8821 over I2S on ACP 7.0), similar to
the ASUS HN7306EA series? Attached: lggram-audio-bug-bundle-v2.tar.gz
(dmesg, dmidecode, asound, lsmod, DSDT.dsl + SSDT excerpts).

I am happy to test patches on 7.0.0-15-generic and mainline.

Thanks,

nawooki