Claude review: drm/bridge: dw-hdmi-qp: Return -EOPNOTSUPP in HDMI audio functions

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**audio_enable refactoring (lines 472-475 after patch):**

```c
	if (!hdmi->tmds_char_rate)
		return -EOPNOTSUPP;

	dw_hdmi_qp_mod(hdmi, 0, AVP_DATAPATH_PACKET_AUDIO_SWDISABLE, GLOBAL_SWDISABLE);
```

Previously, the logic was:

```c
	if (hdmi->tmds_char_rate)
		dw_hdmi_qp_mod(hdmi, 0, AVP_DATAPATH_PACKET_AUDIO_SWDISABLE, GLOBAL_SWDISABLE);

	return 0;
```

The old code returned success (0) even when `tmds_char_rate` was 0 — meaning audio was "enabled" successfully without actually touching the hardware. This is a subtle behavioral change: callers (the `hdmi_codec_startup` path) now see a failure when HDMI is disconnected, rather than a silent no-op success. This is the correct fix — a silent success would allow the ASoC stack to proceed to `get_eld` and `prepare`, which would operate on stale/zero ELD data. By returning `-EOPNOTSUPP` here, the startup aborts cleanly before the ELD path (`hdmi-codec.c:468-482`) is reached, which prevents the "0-valued ELD errors" mentioned in the commit message.

**audio_prepare change (line 489 after patch):**

```c
	if (!hdmi->tmds_char_rate)
		return -EOPNOTSUPP;
```

This is a straightforward error code substitution from `-ENODEV` to `-EOPNOTSUPP`. The guard already existed; only the error code changes.

**Consistency with audio_disable:**

The `dw_hdmi_qp_audio_disable` function (line 526) returns `void` and already has a `tmds_char_rate` guard that simply skips the register writes. No change needed there, and the patch correctly doesn't touch it.

**No issues found.** The patch is minimal, well-scoped, and the commit message accurately explains both the problem and the mechanism. The `-EOPNOTSUPP` choice is validated by `snd_soc_ret()` in `sound/soc/soc-utils.c:30-31` which explicitly skips `dev_err` logging for this error code.

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