No NPU device found on ubuntu

I found this happening on my machine and doing the below fixed it; flm validate reports "No NPU device found" when the real issue is insufficient permissions.

Summary

flm validate prints [ERROR] No NPU device found when the NPU device (/dev/accel/accel0) does exist but the current user lacks permission to open it. This is misleading — the device is present and the amdxdna driver is loaded; the user simply isn't in the render group (or hasn't re-logged after joining it).

Environment

• OS: Ubuntu, kernel 6.17.0-14-generic (Ubuntu 24.04.4 LTS)
• NPU: AMD Device 17F0 (XDNA2) [Strix Halo]
• Driver: amdxdna 0.6.0 (DKMS, out-of-tree)
• FLM version: installed via .deb - fastflowlm_0.9.35_ubuntu24.04_amd64.deb

Steps to Reproduce

1. Install amdxdna-dkms and flm per the Linux guide
2. Do not add your user to the render group (or add them but don't log out/in)
3. Run flm validate

Expected Behavior

A clear error indicating the device exists but access is denied, e.g.:

[Linux]  Kernel: 6.17.0-14-generic
[ERROR]  NPU device found at /dev/accel/accel0 but permission denied.
         Add your user to the 'render' group:  sudo usermod -aG render $USER
         Then log out and log back in.
[Linux]  Memlock Limit: 15992 MB

Actual Behavior

[Linux]  Kernel: 6.17.0-14-generic
[ERROR]  No NPU device found.
[Linux]  Memlock Limit: 15992 MB

flm validate --json similarly reports "amd_device_found": false and "devices": [].

Root Cause

/dev/accel/accel0 is owned by root:render with mode crw-rw----. The sanity_check_npu_stack() function in src/src/main.cpp appears to open the device and, when the open fails with EACCES (permission denied), treats it identically to ENOENT (device not found).

Start in src/src/main.cpp at sanity_check_npu_stack() and reproduce with /dev/accel/accel0 present but inaccessible to the current user. Distinguish permission denial from a missing device in flm validate, including its --json output, and verify that the resulting message gives the render-group guidance shown in the issue.