Claude review: drm/amd/display: Add support for 'link bpc' property

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

Patch Review

**MST exclusion** (correct):

```c
if (!aconnector->mst_root) {
    drm_connector_attach_max_bpc_property(&aconnector->base, 8, 16);
    drm_connector_attach_link_bpc_property(&aconnector->base, 16);
}
```

MST connectors are correctly excluded, matching the existing `max_bpc` behavior. The return value of `drm_connector_attach_link_bpc_property` is silently ignored here, unlike in `drmm_connector_hdmi_init` where it's checked. This is inconsistent — if the property creation fails (e.g. ENOMEM), this silently continues. Consider adding error handling.

**link_bpc set only on stream creation path** (potential gap):

```c
amdgpu_dm_update_link_bpc(drm_new_conn_state,
                          new_stream->timing.display_color_depth);
```

This is called in `dm_update_crtc_state` only when `action == DM_COMMIT_ACTION_DPMS_ON || action == DM_COMMIT_ACTION_SET`. When a connector is disabled (`DPMS_OFF`), `link_bpc` is not reset to 0 or any sentinel, so the property will retain the last active value. This might confuse userspace checking the property on a disconnected output.

**Redundant clamping** (nit):

```c
static void amdgpu_dm_update_link_bpc(struct drm_connector_state *conn_state,
                                      enum dc_color_depth depth)
{
    /* 6 bpc is an experimental internal format only, use 8 as minimum */
    conn_state->link_bpc = clamp(convert_dc_color_depth_into_bpc(depth), 8,
                                 conn_state->max_bpc);
}
```

The clamping is also done in `drm_connector_update_link_bpc_property()`, making this double-clamped. While not harmful, it's worth noting. The comment about 6 bpc being experimental is helpful though.

**`convert_dc_color_depth_into_bpc` can return 0**: If `depth` is an unexpected `dc_color_depth` enum value, the function returns 0. After clamping with min=8, this would become 8, which is a reasonable fallback. However, it might be worth adding a `drm_dbg` when the conversion returns 0, as it would indicate an unexpected hardware state.

---
Generated by Claude Code Patch Reviewer