Claude review: drm: renesas: rz-du: Make DU reset control optional for RZ/T2H support

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

Patch Review

The change itself is a single-line diff:

```c
-	rcrtc->rstc = devm_reset_control_get_shared(rcdu->dev, NULL);
+	rcrtc->rstc = devm_reset_control_get_optional_shared(rcdu->dev, NULL);
```

**Issue 1 — NULL reset not guarded in callers:**

When the reset is optional, `devm_reset_control_get_optional_shared()` returns `NULL` if no reset is specified in DT. The error path immediately after:

```c
	if (IS_ERR(rcrtc->rstc)) {
		dev_err(rcdu->dev, "can't get cpg reset\n");
		return PTR_ERR(rcrtc->rstc);
	}
```

This correctly handles the `IS_ERR` case, and `NULL` will pass through (not an error). However, we need to verify that all callers of `rcrtc->rstc` handle `NULL` safely. The reset control API (`reset_control_deassert`, `reset_control_assert`) does handle `NULL` arguments gracefully (they're no-ops), so this should be safe. This is fine.

**Issue 2 — Ordering concern:**

This patch makes the reset optional unconditionally for all SoCs, but the DT binding in patch 1 uses `resets: false` to forbid it only on T2H. The driver change is broader than the binding constraint, which is acceptable since the optional API is safe for all variants. But the commit message should clarify that the reset API itself is NULL-safe, so existing SoCs with resets continue to work unchanged.

**Minor — Error message is now misleading:**

The error log `"can't get cpg reset\n"` still triggers on failure, but since the reset is optional, the error path only fires for actual errors (not absence). This is fine, but the message could note it's a lookup error vs. absence.

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Generated by Claude Code Patch Reviewer