[Cezanne/Green Sardine] `amdgpu_read_mm_registers` function always succeeds

Brief summary of the problem:

amdgpu_read_mm_registers(
                device_handle,
                offset,
                1, // count
                0xFFFF_FFFF, // instance mask, full mask
                0, // flags
                &out,
            )

When the above function is called via libdrm_amdgpu, it returns an error (-14) if register offset is not allowed, but in Cezanne/GreenSardine APU it always succeeds. (even if the register offset is a value such as 0xDEAD_BEEF)
In the case of Polaris11, it returns an error normally for register offsets that are not allowed.

• amdgpu_allowed_register_entry
  • /drivers/gpu/drm/amd/amdgpu/vi.c
• soc15_allowed_register_entry
  • /drivers/gpu/drm/amd/amdgpu/soc15.c

Hardware description:

• CPU: Ryzen 5 5600G
• GPU: AMD Radeon Graphics (0x1638:0xC9)
• System Memory: DDR4 16GB

System information:

• Kernel version: v6.1.13
• drm version: 3.49.0

How to reproduce the issue:

• test code: https://github.com/Umio-Yasuno/libdrm-amdgpu-sys-rs/blob/test-read-reg/examples/read_reg.rs
• Command: cargo run --example read_reg