Claude review: drm/dp: Add DSC virtual DPCD quirk for Realtek MST branch device

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

Patch Review

**Code change:**
```c
/* Realtek DP1.4 MST hubs can support DSC without virtual DPCD */
{ OUI(0x00, 0xe0, 0x4c), DEVICE_ID('D', 'p', '1', '.', '4', 0), true, BIT(DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) },
```

**Observations:**

1. **Correct placement**: The new entry is inserted directly after the existing Synaptics `DSC_WITHOUT_VIRTUAL_DPCD` entry (line 2548), grouping related quirks together. Good.

2. **OUI `00:e0:4c`**: This is Realtek's registered IEEE OUI. Correct.

3. **Specific device ID vs. DEVICE_ID_ANY**: Unlike the Synaptics entry which uses `DEVICE_ID_ANY` (matching all Synaptics branch devices), this patch specifies a particular device ID string `"Dp1.4\0"`. This is a more conservative approach — it limits the quirk to only the specific Realtek device that has been tested, rather than all Realtek MST hubs. This is appropriate since Realtek may ship other MST devices where this quirk might not apply.

4. **Null byte in device ID**: The sixth byte is `0` (null), not a printable character. Looking at the quirk matching logic in `drm_dp_get_quirks()` (line 2590-2591), the device_id comparison uses `memcmp` over the full 6-byte array, so a null byte is compared correctly — it's treated as data, not a string terminator. No issue here.

5. **`is_branch = true`**: Correct — this is an MST branch device (hub), not a sink.

6. **Commit message quality**: The commit message properly explains the problem (no discoverable peer-to-peer virtual device), the hardware context (ASUS DC301 dock with Realtek MST), and the solution (reuse the existing quirk). It includes `Reported-and-tested-by` and `Cc` tags appropriately.

**No issues found.** This is a clean, minimal, well-tested quirk addition following established patterns.

Reviewed-by criteria: **Acceptable as-is.**

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Generated by Claude Code Patch Reviewer