How can I managed the physical memory cacheability setting for a memory region in machine mode software

**Type of issue**: bug report | feature request | other enhancement

**Impact**: no functional change | API addition (no impact on existing code) | API modification | unknown

**Development Phase**: request | proposal

**Other information**

**If the current behavior is a bug, please provide the steps to reproduce the problem:**

**What is the current behavior?**

**What is the expected behavior?**

**Please tell us about your environment:**

**What is the use case for changing the behavior?**

The issue names no files, tests, reproduction steps, environment, or expected behavior. Start by clarifying whether this is a feature request or a support question, then provide a concrete cacheability use case and affected Rocket Chip configuration. The scope and definition of done cannot be established until those details are supplied.

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