feat: experimental NVIDIA power control via RM ioctl interface

Adds an experimental power-cap mode using the undocumented RM ioctl
interface (based on panchovix's LACT PR #1205) to set power limits
below the VBIOS minimum (down to 30 W).

- hal/rm_power.py: RM ioctl power-cap read/write/reset + runtime probe
- limits.py: power_cap_mode (nvml/ioctl) with support detection
- config.py: persist power_cap_mode per GPU
- profiles: record/apply power_cap_mode
- server.py: POST /api/limits validates ioctl support (409 on failure)
- cli.py: profile save falls back to persisted mode
- client.py: power_cap_mode in Limits
- frontend: toggle + warning with panchovix attribution (LACT #1205)
- tests: test_rm_power.py (unit) + integration coverage
- Makefile: add test_rm_power.py to make test

Also includes automated linter reformatting (prettier, ruff, shellcheck,
isort, markdownlint) that the linter would apply anyway.

nvcurve/cli.py

@@ -405,6 +405,11 @@ def run_diagnostics(gpu, gpu_name, gpu_index: int = 0):
     print(f"  Default:  {fmt_w(def_w)}")
     if min_w is not None and max_w is not None:
         print(f"  Range:    {min_w} – {max_w} W")
+    if pwr.get("rm_power_supported"):
+        print(
+            "  Experimental RM power: available (opt-in via web UI or profile;"
+            " extends range to 30 W)"
+        )
 
 
 # ── Privilege / browser helpers ───────────────────────────────────────────────
@@ -1207,12 +1212,33 @@ def cmd_profile(args):
             power_limit_w = None
             mem_offset_mhz = None
 
+        # Capture the GPU's power-cap mode: prefer the running server (most
+        # current), else fall back to the persisted per-GPU mode from config
+        # (so a profile saved while the server is down or auth is enabled
+        # still records the GPU's actual mode rather than assuming nvml).
+        power_cap_mode = "nvml"
+        try:
+            from .client import NvCurveClient
+
+            base = getattr(args, "server", None) or _discover_server_url(default_config)
+            limits = NvCurveClient(base=base, gpu_index=gpu_index).limits()
+            if limits.get("power_cap_mode") in ("nvml", "ioctl"):
+                power_cap_mode = limits["power_cap_mode"]
+        except Exception as exc:
+            log.debug("Could not read power-cap mode from server: %s", exc)
+            gpu_key = _gpu_stable_key_offline(gpu_index)
+            if gpu_key is not None:
+                persisted = default_config.power_cap_modes.get(gpu_key)
+                if persisted in ("nvml", "ioctl"):
+                    power_cap_mode = persisted
+
         data = ProfileData(
             name=args.name,
             gpu_name=gpu_name,
             curve_deltas=curve_deltas,
             mem_offset_mhz=mem_offset_mhz,
             power_limit_w=power_limit_w,
+            power_cap_mode=power_cap_mode,
         )
         filepath = save_profile(default_config.profile_dir, data)
         print(f"Saved profile '{args.name}' to {filepath}")
@@ -1249,7 +1275,8 @@ def cmd_profile(args):
                 errs.append(f"Mem offset: {msg}")
 
         if profile.power_limit_w is not None:
-            ok, msg = set_power_limit(profile.power_limit_w, gpu_index)
+            mode = profile.power_cap_mode or "nvml"
+            ok, msg = set_power_limit(profile.power_limit_w, gpu_index, mode)
             if not ok:
                 errs.append(f"Power limit: {msg}")
 
@@ -2296,6 +2323,14 @@ def main():
             if "fan_curves" in data:
                 # Per-GPU active fan curves, restored on server startup.
                 cfg.fan_curves = dict(data["fan_curves"])
+            if "power_cap_modes" in data:
+                # Per-GPU experimental power-cap mode. "nvml" is the default
+                # (the server treats it as unset); keep only valid values.
+                cfg.power_cap_modes = {
+                    str(k): str(v)
+                    for k, v in dict(data["power_cap_modes"]).items()
+                    if str(v) in ("nvml", "ioctl")
+                }
     except Exception as exc:
         log.debug("Could not load user config: %s", exc)
 

nvcurve/client.py

@@ -145,6 +145,9 @@ class NvCurveClient:
     def snapshots(self) -> list:
         return self._get("/api/snapshots")
 
+    def limits(self) -> dict:
+        return self._get("/api/limits")
+
     # ── Profiles ─────────────────────────────────────────────────────────────
 
     def profiles(self) -> dict:

nvcurve/config.py

@@ -54,6 +54,11 @@ class Config:
     # Legacy entries (bare curve list) are migrated at load time.
     fan_curves: dict[str, object] = field(default_factory=dict)
 
+    # Per-GPU power-cap mode: "nvml" (default, never stored) or "ioctl"
+    # (experimental RM power control — permits caps below the VBIOS minimum).
+    # Key = stable GPU identifier (same as auto_load_profiles).
+    power_cap_modes: dict[str, str] = field(default_factory=dict)
+
 
 # Module-level default config instance.
 default_config = Config()

nvcurve/hal/limits.py

@@ -59,20 +59,37 @@ def _get_handle(gpu_index: int):
 # ── Power limit ───────────────────────────────────────────────────────────────
 
 
-def get_power_limit(gpu_index: int = 0) -> dict:
-    """Return dict with power_limit_w, default_power_limit_w, min_power_limit_w, max_power_limit_w."""
-    out: dict[str, int | None] = {
+def get_power_limit(gpu_index: int = 0, mode: str = "nvml") -> dict:
+    """Return dict with power limit info.
+
+    Keys: power_limit_w, default_power_limit_w, min_power_limit_w,
+    min_power_limit_w_native, max_power_limit_w, rm_power_supported,
+    power_cap_mode.
+
+    mode: "nvml" (default) or "ioctl" (experimental RM power control).
+    min_power_limit_w is the effective minimum: in ioctl mode it is
+    extended to the experimental floor (30 W) when the RM interface is
+    present and validated; min_power_limit_w_native is always the VBIOS
+    minimum. The RM probe is GET-only (no writes) and safe to run on
+    every call.
+    """
+    out: dict[str, int | bool | str | None] = {
         "power_limit_w": None,
         "default_power_limit_w": None,
         "min_power_limit_w": None,
+        "min_power_limit_w_native": None,
         "max_power_limit_w": None,
+        "rm_power_supported": False,
+        "power_cap_mode": mode,
     }
     try:
         handle = _get_handle(gpu_index)
         limit = pynvml.nvmlDeviceGetPowerManagementLimit(handle)
         constrs = pynvml.nvmlDeviceGetPowerManagementLimitConstraints(handle)
         out["power_limit_w"] = limit // 1000
-        out["min_power_limit_w"] = constrs[0] // 1000
+        native_min = constrs[0] // 1000
+        out["min_power_limit_w"] = native_min
+        out["min_power_limit_w_native"] = native_min
         out["max_power_limit_w"] = constrs[1] // 1000
         try:
             default = pynvml.nvmlDeviceGetPowerManagementDefaultLimit(handle)
@@ -81,11 +98,39 @@ def get_power_limit(gpu_index: int = 0) -> dict:
             log.debug("nvmlDeviceGetPowerManagementDefaultLimit: %s", exc)
     except Exception as exc:
         log.warning("get_power_limit: %s", exc)
+        return out
+
+    # GET-only RM discovery — reported so the UI can offer the experimental
+    # mode; the effective minimum only changes in ioctl mode.
+    try:
+        from . import rm_power
+
+        bounds = rm_power.probe_gpu(gpu_index)
+        out["rm_power_supported"] = bounds is not None
+        if bounds is not None and mode == "ioctl":
+            out["min_power_limit_w"] = bounds.lower_min_mw() // 1000
+    except Exception as exc:
+        log.debug("RM power probe failed: %s", exc)
     return out
 
 
-def set_power_limit(limit_w: int, gpu_index: int = 0) -> tuple[bool, str]:
-    """Set the board power limit (Watts)."""
+def set_power_limit(
+    limit_w: int, gpu_index: int = 0, mode: str = "nvml"
+) -> tuple[bool, str]:
+    """Set the board power limit (Watts).
+
+    mode "ioctl" (experimental) applies the limit through the undocumented
+    RM interface, which permits values below the VBIOS minimum. It has no
+    fallback: failures are reported, never silently switched to NVML.
+    """
+    if mode == "ioctl":
+        from . import rm_power
+
+        try:
+            rm_power.set_power_limit_w(gpu_index, limit_w)
+            return True, "OK"
+        except rm_power.RmPowerError as exc:
+            return False, str(exc)
     try:
         handle = _get_handle(gpu_index)
         pynvml.nvmlDeviceSetPowerManagementLimit(handle, limit_w * 1000)

nvcurve/hal/rm_power.py

@@ -0,0 +1,627 @@
+"""Undocumented NVIDIA RM power-limit interface (EXPERIMENTAL).
+
+Port of the approach from LACT PR #1205 (ilya-zlobintsev/LACT): applies board
+power limits through the private NV2080 power-limit "ordinary client"
+interface on /dev/nvidiactl, which permits caps below the VBIOS minimum
+(down to 30 W). The native maximum still applies.
+
+EXPERIMENTAL — uses an undocumented driver interface. It may break after
+driver updates. Discovery is GET-only and validates the RM payload against
+NVML before any write is issued; a failed write restores the previous
+request (even if it was below the VBIOS minimum).
+"""
+
+from __future__ import annotations
+
+import contextlib
+import ctypes
+import fcntl
+import logging
+import os
+import struct
+import sys
+from collections.abc import Callable
+from dataclasses import dataclass
+
+log = logging.getLogger("nvcurve.hal.rm_power")
+
+# ── ioctl constants (nv-ioctl.h / nv-ioctl-numbers.h) ─────────────────────────
+
+NV_IOCTL_MAGIC = ord("N")  # 0x4E — user-space RM interface
+NV_ESC_RM_ALLOC = 0x2B
+NV_ESC_RM_CONTROL = 0x2A
+
+# 'F' magic interface (kernel-open/common/inc/nv-ioctl-numbers.h) —
+# NV_ESC_REGISTER_FD lives here, not in the 'N' RM interface.
+NV_IOCTL_MAGIC_F = ord("F")  # 0x46
+NV_IOCTL_BASE_F = 200
+NV_ESC_REGISTER_FD = NV_IOCTL_BASE_F + 1  # 201
+
+# RM class IDs (nv0080.h / nv2080.h)
+NV01_DEVICE_0 = 0x0080
+NV20_SUBDEVICE_0 = 0x2080
+
+# NV01_ROOT GPU queries (ctrl0000gpu.h) — resolve PCI identity to the RM
+# device/subdevice instance numbers used by NV0080 and NV2080 allocations;
+# neither number is a Linux device minor.
+_CTRL_GPU_GET_ATTACHED_IDS = 0x201
+_CTRL_GPU_GET_ID_INFO_V2 = 0x205
+_CTRL_GPU_GET_PCI_INFO = 0x21B
+_MAX_GPUS = 32
+_INVALID_GPU_ID = 0xFFFFFFFF
+
+# Private NV2080 power-limit client commands. Payloads compared against
+# NvAPI and GSP from R595, R610 and R615 (native RM payloads, without
+# NvAPI's 0x10-byte transport prefix).
+_PWR_GET_INFO = 0x2080_A630
+_PWR_GET_CONTROL = 0x2080_A632
+_PWR_SET_CONTROL = 0x2080_E633
+_ORDINARY_CLIENT = 0xFE
+_LOWER_LIMIT_MW = 30_000  # experimental floor: 30 W
+
+
+def _ioctl_rw(size: int, nr: int, magic: int = NV_IOCTL_MAGIC) -> int:
+    """Linux ioctl request code: dir=RW, given size/type/nr."""
+    return (2 << 30) | (size << 16) | (magic << 8) | nr
+
+
+def _ioctl_call(fd: int, code: int, arg) -> None:
+    """Issue an ioctl, converting errno failures to RmPowerError.
+
+    The driver normally reports failures as an RM status in the parameter
+    struct, but an experimental interface can also fail at the kernel level
+    (ENOTTY/EBADF/EPERM across driver versions). Converting to RmPowerError
+    keeps the module's error contract uniform and lets callers clean up fds.
+    """
+    try:
+        fcntl.ioctl(fd, code, arg)
+    except OSError as exc:
+        raise RmPowerError(f"ioctl 0x{code:x} failed: {exc}") from exc
+
+
+# ── NVOS parameter structs (nvos.h) ──────────────────────────────────────────
+
+
+class _NVOS21(ctypes.Structure):
+    _fields_ = [
+        ("hRoot", ctypes.c_uint32),
+        ("hObjectParent", ctypes.c_uint32),
+        ("hObjectNew", ctypes.c_uint32),
+        ("hClass", ctypes.c_uint32),
+        ("pAllocParms", ctypes.c_uint64),
+        ("paramsSize", ctypes.c_uint32),
+        ("status", ctypes.c_uint32),
+    ]
+
+
+class _NVOS64(ctypes.Structure):
+    _fields_ = [
+        ("hRoot", ctypes.c_uint32),
+        ("hObjectParent", ctypes.c_uint32),
+        ("hObjectNew", ctypes.c_uint32),
+        ("hClass", ctypes.c_uint32),
+        ("pAllocParms", ctypes.c_uint64),
+        ("pRightsRequested", ctypes.c_uint64),
+        ("paramsSize", ctypes.c_uint32),
+        ("flags", ctypes.c_uint32),
+        ("status", ctypes.c_uint32),
+    ]
+
+
+class _NVOS54(ctypes.Structure):
+    _fields_ = [
+        ("hClient", ctypes.c_uint32),
+        ("hObject", ctypes.c_uint32),
+        ("cmd", ctypes.c_uint32),
+        ("flags", ctypes.c_uint32),
+        ("params", ctypes.c_uint64),
+        ("paramsSize", ctypes.c_uint32),
+        ("status", ctypes.c_uint32),
+    ]
+
+
+class _NV0080_ALLOC(ctypes.Structure):
+    _fields_ = [
+        ("deviceId", ctypes.c_uint32),
+        ("deviceFlags", ctypes.c_uint32),
+        ("vgpuInstance", ctypes.c_uint32),
+        ("pad", ctypes.c_uint32),
+    ]
+
+
+class _NV2080_ALLOC(ctypes.Structure):
+    _fields_ = [
+        ("subDeviceId", ctypes.c_uint32),
+        ("clientShare", ctypes.c_uint32),
+        ("flags", ctypes.c_uint32),
+        ("pad", ctypes.c_uint32),
+    ]
+
+
+# ── Errors ───────────────────────────────────────────────────────────────────
+
+
+class RmPowerError(RuntimeError):
+    """Raised when the RM power-limit interface is unavailable or fails."""
+
+
+# ── Power-limit layouts and bounds ───────────────────────────────────────────
+
+
+@dataclass(frozen=True)
+class PowerLimitLayout:
+    """Byte offsets of the private power-limit payloads for one wire format."""
+
+    name: str
+    info_size: int
+    control_size: int
+    info_min_at: int
+    request_at: int
+    client_at: int
+    mask_end: int
+
+
+EXTENDED_LAYOUT = PowerLimitLayout(
+    name="extended",
+    info_size=0x924,
+    control_size=0x328,
+    info_min_at=0x28,
+    request_at=0x2C,
+    client_at=0x30,
+    mask_end=0x24,
+)
+LEGACY_LAYOUT = PowerLimitLayout(
+    name="legacy",
+    info_size=0x488,
+    control_size=0x188,
+    info_min_at=0xC,
+    request_at=0xC,
+    client_at=0x10,
+    mask_end=0x8,
+)
+
+
+@dataclass(frozen=True)
+class PowerLimitBounds:
+    """Power limit bounds in milliwatts (NVML/RM units)."""
+
+    min_mw: int
+    default_mw: int
+    max_mw: int
+
+    def lower_min_mw(self) -> int:
+        """Effective minimum when the experimental route is active."""
+        return min(self.min_mw, _LOWER_LIMIT_MW)
+
+
+@dataclass(frozen=True)
+class LowerPowerLimit:
+    """A validated RM power-limit layout that can be written."""
+
+    bounds: PowerLimitBounds
+    layout: PowerLimitLayout
+
+    def lower_min_mw(self) -> int:
+        return self.bounds.lower_min_mw()
+
+
+# ── PCI identity → RM instance resolution ────────────────────────────────────
+
+
+@dataclass(frozen=True)
+class PciLocation:
+    domain: int
+    bus: int
+    dev: int
+    func: int = 0
+
+
+def resolve_gpu_instance(
+    pci: PciLocation,
+    query: Callable[[int, bytearray], None],
+) -> tuple[int, int]:
+    """Resolve (device_instance, subdevice_instance) by PCI identity.
+
+    /dev/nvidiaN minors and RM device instances can have different orders;
+    the RM object must be matched by PCI domain/bus/slot, not by index.
+    The RM query exposes domain/bus/slot but no PCI function, so only
+    function-zero devices can be matched (never another function of a
+    multifunction device).
+    """
+    if pci.func != 0:
+        raise RmPowerError("RM GPU lookup requires PCI function zero")
+
+    attached = bytearray(_MAX_GPUS * 4)
+    query(_CTRL_GPU_GET_ATTACHED_IDS, attached)
+
+    for i in range(_MAX_GPUS):
+        gpu_id = struct.unpack_from("<I", attached, i * 4)[0]
+        if gpu_id == _INVALID_GPU_ID:
+            continue
+
+        # NV0000_CTRL_GPU_GET_PCI_INFO_PARAMS: u32 gpuId, u32 domain,
+        # u16 bus, u16 slot.
+        location = bytearray(12)
+        location[0:4] = struct.pack("<I", gpu_id)
+        query(_CTRL_GPU_GET_PCI_INFO, location)
+        domain, bus, slot = struct.unpack_from("<IHH", location, 4)
+        if (domain, bus, slot) != (pci.domain, pci.bus, pci.dev):
+            continue
+
+        # NV0000_CTRL_GPU_GET_ID_INFO_V2_PARAMS: eight u32 fields, with
+        # deviceInstance/subDeviceInstance at +8/+12.
+        info = bytearray(32)
+        info[0:4] = struct.pack("<I", gpu_id)
+        query(_CTRL_GPU_GET_ID_INFO_V2, info)
+        device, subdevice = struct.unpack_from("<II", info, 8)
+        return device, subdevice
+
+    raise RmPowerError(f"no RM GPU matches PCI location {pci}")
+
+
+# ── RM handle ────────────────────────────────────────────────────────────────
+
+
+def _rm_control(fd: int, client: int, obj: int, cmd: int, buf: bytearray) -> None:
+    """Issue an NVOS54 RM control whose parameter block is a byte buffer."""
+    arr = (ctypes.c_uint8 * len(buf)).from_buffer(buf)
+    req = _NVOS54(
+        hClient=client,
+        hObject=obj,
+        cmd=cmd,
+        flags=0,
+        params=ctypes.addressof(arr),
+        paramsSize=len(buf),
+        status=0,
+    )
+    _ioctl_call(fd, _ioctl_rw(ctypes.sizeof(_NVOS54), NV_ESC_RM_CONTROL), req)
+    if req.status != 0:
+        raise RmPowerError(
+            f"RM control 0x{cmd:08x} failed with status 0x{req.status:x}"
+        )
+
+
+def _alloc_client(fd: int) -> int:
+    """Allocate an RM client (NVOS21, all-zero parameters)."""
+    req = _NVOS21()
+    _ioctl_call(fd, _ioctl_rw(ctypes.sizeof(_NVOS21), NV_ESC_RM_ALLOC), req)
+    if req.status != 0:
+        raise RmPowerError(f"could not allocate RM client (status 0x{req.status:x})")
+    return req.hObjectNew
+
+
+def _alloc_object(
+    fd: int, client: int, parent: int, class_id: int, alloc_params: ctypes.Structure
+) -> int:
+    """Allocate an RM object (NVOS64) and return its handle."""
+    req = _NVOS64(
+        hRoot=client,
+        hObjectParent=parent,
+        hObjectNew=0,
+        hClass=class_id,
+        pAllocParms=ctypes.addressof(alloc_params),
+        pRightsRequested=0,
+        paramsSize=ctypes.sizeof(alloc_params),
+        flags=0,
+        status=0,
+    )
+    _ioctl_call(fd, _ioctl_rw(ctypes.sizeof(_NVOS64), NV_ESC_RM_ALLOC), req)
+    if req.status != 0:
+        raise RmPowerError(
+            f"RM class 0x{class_id:x} allocation failed (status 0x{req.status:x})"
+        )
+    return req.hObjectNew
+
+
+def _register_fd(device_fd: int, nvidiactl_fd: int) -> None:
+    """Register the nvidiactl client with the device fd (NV_ESC_REGISTER_FD).
+
+    The ioctl is issued on the /dev/nvidiaN fd; the argument is the
+    nvidiactl fd to associate with it.
+    """
+    _ioctl_call(
+        device_fd,
+        _ioctl_rw(4, NV_ESC_REGISTER_FD, NV_IOCTL_MAGIC_F),
+        struct.pack("i", nvidiactl_fd),
+    )
+
+
+class RmHandle:
+    """An NVIDIA RM client with device + subdevice objects for one GPU."""
+
+    def __init__(
+        self,
+        nvidiactl_fd: int,
+        device_fd: int,
+        client_handle: int,
+        device_handle: int,
+        subdevice_handle: int,
+    ) -> None:
+        self._nvidiactl_fd = nvidiactl_fd
+        self._device_fd = device_fd
+        self.client_handle = client_handle
+        self.device_handle = device_handle
+        self.subdevice_handle = subdevice_handle
+
+    @classmethod
+    def open(cls, gpu_index: int) -> RmHandle:
+        """Open an RM handle for the GPU at the given NVML index.
+
+        The RM device/subdevice instances are resolved by PCI identity
+        (minors and RM instances can have different orders).
+        """
+        pynvml = _ensure_nvml()
+
+        try:
+            handle = pynvml.nvmlDeviceGetHandleByIndex(gpu_index)
+            minor = int(pynvml.nvmlDeviceGetMinorNumber(handle))
+            pci_info = pynvml.nvmlDeviceGetPciInfo(handle)
+            pci = PciLocation(
+                domain=int(pci_info.domain),
+                bus=int(pci_info.bus),
+                dev=int(pci_info.device),
+            )
+        except Exception as exc:
+            raise RmPowerError(f"NVML query for GPU {gpu_index} failed: {exc}") from exc
+
+        try:
+            nvidiactl_fd = os.open("/dev/nvidiactl", os.O_RDWR)
+        except OSError as exc:
+            raise RmPowerError(f"could not open /dev/nvidiactl: {exc}") from exc
+
+        try:
+            client_handle = _alloc_client(nvidiactl_fd)
+            device_instance, subdevice_instance = resolve_gpu_instance(
+                pci,
+                lambda cmd, buf: _rm_control(
+                    nvidiactl_fd, client_handle, client_handle, cmd, buf
+                ),
+            )
+        except RmPowerError:
+            os.close(nvidiactl_fd)
+            raise
+
+        try:
+            device_fd = os.open(f"/dev/nvidia{minor}", os.O_RDWR)
+        except OSError as exc:
+            os.close(nvidiactl_fd)
+            raise RmPowerError(f"could not open /dev/nvidia{minor}: {exc}") from exc
+
+        try:
+            _register_fd(device_fd, nvidiactl_fd)
+            device_handle = _alloc_object(
+                nvidiactl_fd,
+                client_handle,
+                client_handle,
+                NV01_DEVICE_0,
+                _NV0080_ALLOC(deviceId=device_instance),
+            )
+            subdevice_handle = _alloc_object(
+                nvidiactl_fd,
+                client_handle,
+                device_handle,
+                NV20_SUBDEVICE_0,
+                _NV2080_ALLOC(subDeviceId=subdevice_instance),
+            )
+        except RmPowerError:
+            os.close(device_fd)
+            os.close(nvidiactl_fd)
+            raise
+
+        return cls(
+            nvidiactl_fd, device_fd, client_handle, device_handle, subdevice_handle
+        )
+
+    def control(self, cmd: int, buf: bytearray) -> None:
+        """Issue an NVOS54 RM control on the subdevice with a byte buffer."""
+        _rm_control(
+            self._nvidiactl_fd, self.client_handle, self.subdevice_handle, cmd, buf
+        )
+
+    def close(self) -> None:
+        """Close the fds; the driver reclaims the RM client objects."""
+        with contextlib.suppress(OSError):
+            os.close(self._device_fd)
+        with contextlib.suppress(OSError):
+            os.close(self._nvidiactl_fd)
+
+
+# ── Power-limit probe / set (pure logic, testable with a fake query) ─────────
+
+
+def _u32(data: bytearray | bytes, offset: int) -> int:
+    return struct.unpack_from("<I", data, offset)[0]
+
+
+def _validate_header(layout: PowerLimitLayout, data: bytearray) -> None:
+    if _u32(data, 0) != 0xFF or _u32(data, 4) != 1:
+        raise RmPowerError("unrecognized RM power client layout")
+    # The extended layout has additional mask words; accepting only its low
+    # word would allow an unexpected client to be included in a later SET.
+    if any(byte != 0 for byte in data[8 : layout.mask_end]):
+        raise RmPowerError("unrecognized RM power client layout")
+
+
+def _read_bounds(
+    layout: PowerLimitLayout, query: Callable[[int, bytearray], None]
+) -> PowerLimitBounds:
+    info = bytearray(layout.info_size)
+    query(_PWR_GET_INFO, info)
+    _validate_header(layout, info)
+    bounds = PowerLimitBounds(
+        min_mw=_u32(info, layout.info_min_at),
+        default_mw=_u32(info, layout.info_min_at + 4),
+        max_mw=_u32(info, layout.info_min_at + 8),
+    )
+    if not (
+        bounds.min_mw > 0
+        and bounds.min_mw <= bounds.default_mw
+        and bounds.default_mw <= bounds.max_mw
+    ):
+        raise RmPowerError("invalid RM power limit bounds")
+    return bounds
+
+
+def _read_control(
+    layout: PowerLimitLayout, query: Callable[[int, bytearray], None]
+) -> bytearray:
+    control = bytearray(layout.control_size)
+    control[4:8] = struct.pack("<I", 1)
+    control[layout.client_at] = _ORDINARY_CLIENT
+    query(_PWR_GET_CONTROL, control)
+    _validate_header(layout, control)
+    if control[layout.client_at] != _ORDINARY_CLIENT:
+        raise RmPowerError("unexpected power client")
+    if _u32(control, layout.request_at) in (0, 0xFFFFFFFF):
+        raise RmPowerError("no ordinary power request available")
+    return control
+
+
+def probe(
+    nvml_bounds: PowerLimitBounds,
+    nvml_current_mw: int,
+    query: Callable[[int, bytearray], None],
+) -> LowerPowerLimit:
+    """GET-only discovery of the RM power-limit layout.
+
+    Probes the two known wire formats using GETs only. A driver version
+    number is not evidence that the payload still has the same layout or
+    units, so the bounds and the current request are validated against
+    NVML. Discovery never issues a SET.
+    """
+    if sys.byteorder != "little":
+        raise RmPowerError("little-endian host required")
+    errors: list[str] = []
+    for layout in (EXTENDED_LAYOUT, LEGACY_LAYOUT):
+        try:
+            bounds = _read_bounds(layout, query)
+            if bounds != nvml_bounds:
+                raise RmPowerError("RM power bounds differ from NVML")
+            control = _read_control(layout, query)
+            if _u32(control, layout.request_at) != nvml_current_mw:
+                raise RmPowerError("RM ordinary power request differs from NVML")
+            return LowerPowerLimit(bounds=bounds, layout=layout)
+        except RmPowerError as exc:
+            errors.append(f"{layout.name}: {exc}")
+    raise RmPowerError("no compatible RM power layout: " + "; ".join(errors))
+
+
+def set_limit(
+    limit_mw: int,
+    support: LowerPowerLimit,
+    query: Callable[[int, bytearray], None],
+) -> None:
+    """Set the ordinary-client power request with readback verification.
+
+    Keeps the entire current payload, changing only entry 0's request.
+    Mask 1 and selector 0xFE prevent modifying any other entry or the
+    additional F8 client. A failed SET can have side effects, so the
+    previous request is restored even on transport failure — and the
+    restore uses 0xFE so a previous limit below the VBIOS minimum can
+    also be restored.
+    """
+    layout = support.layout
+    bounds = _read_bounds(layout, query)
+    if bounds != support.bounds:
+        raise RmPowerError("RM power bounds changed since discovery")
+    lower = bounds.lower_min_mw()
+    if not (lower <= limit_mw <= bounds.max_mw):
+        raise RmPowerError(
+            f"power limit {limit_mw} mW outside supported range "
+            f"{lower}..{bounds.max_mw} mW"
+        )
+
+    before = _read_control(layout, query)
+    if _u32(before, layout.request_at) == limit_mw:
+        return
+
+    expected = bytearray(before)
+    expected[layout.request_at : layout.request_at + 4] = struct.pack("<I", limit_mw)
+
+    try:
+        request = bytearray(expected)
+        query(_PWR_SET_CONTROL, request)
+        if _read_control(layout, query) != expected:
+            raise RmPowerError("power request readback differs")
+    except RmPowerError as apply_error:
+        try:
+            restore = bytearray(before)
+            query(_PWR_SET_CONTROL, restore)
+            if _read_control(layout, query) != before:
+                raise RmPowerError("restored power request differs")
+        except RmPowerError as restore_error:
+            raise RmPowerError(
+                f"power request failed: {apply_error}; "
+                f"restoration also failed: {restore_error}"
+            ) from None
+        raise RmPowerError(f"{apply_error} (previous power request restored)") from None
+
+
+# ── High-level API (wires NVML state + RmHandle to the pure logic) ───────────
+
+
+def _ensure_nvml():
+    """Return pynvml with NVML initialized (nvmlInit is refcounted)."""
+    import pynvml
+
+    pynvml.nvmlInit()
+    return pynvml
+
+
+def _nvml_power_state(gpu_index: int) -> tuple[PowerLimitBounds, int]:
+    """Return (bounds, current_mw) from NVML for the given GPU."""
+    pynvml = _ensure_nvml()
+
+    try:
+        handle = pynvml.nvmlDeviceGetHandleByIndex(gpu_index)
+        min_mw, max_mw = pynvml.nvmlDeviceGetPowerManagementLimitConstraints(handle)
+        default_mw = pynvml.nvmlDeviceGetPowerManagementDefaultLimit(handle)
+        current_mw = pynvml.nvmlDeviceGetPowerManagementLimit(handle)
+        bounds = PowerLimitBounds(int(min_mw), int(default_mw), int(max_mw))
+        current = int(current_mw)
+    except Exception as exc:
+        raise RmPowerError(
+            f"NVML power state for GPU {gpu_index} unavailable: {exc}"
+        ) from exc
+    return bounds, current
+
+
+def probe_gpu(gpu_index: int = 0) -> PowerLimitBounds | None:
+    """GET-only discovery of the RM power-limit interface for a GPU.
+
+    Returns the validated power bounds (milliwatts) when a compatible RM
+    layout is present, else None. Never issues a write.
+    """
+    try:
+        bounds, current = _nvml_power_state(gpu_index)
+    except Exception as exc:
+        log.debug("RM probe: NVML state unavailable: %s", exc)
+        return None
+    try:
+        handle = RmHandle.open(gpu_index)
+    except RmPowerError as exc:
+        log.debug("RM probe: handle open failed: %s", exc)
+        return None
+    try:
+        probe(bounds, current, handle.control)
+        return bounds
+    except RmPowerError as exc:
+        log.debug("RM probe: %s", exc)
+        return None
+    finally:
+        handle.close()
+
+
+def set_power_limit_w(gpu_index: int, limit_w: int) -> None:
+    """Set the board power limit (watts) via the RM interface.
+
+    Raises RmPowerError on any failure (probe, range, write, readback).
+    A failed write restores the previous request.
+    """
+    bounds, current = _nvml_power_state(gpu_index)
+    handle = RmHandle.open(gpu_index)
+    try:
+        support = probe(bounds, current, handle.control)
+        set_limit(int(limit_w) * 1000, support, handle.control)
+    finally:
+        handle.close()

nvcurve/nvapi/bootstrap.py

@@ -9,7 +9,7 @@ from .errors import NVAPI_ERRORS
 
 def load_nvapi() -> ctypes.CDLL:
     """Load libnvidia-api.so from the NVIDIA driver."""
-    for name in ("libnvidia-api.so", "libnvidia-api.so.1"):
+    for name in ("libnvidia-api.so", "libnvidia-api.so.1"):  # gitleaks:allow
         try:
             return ctypes.CDLL(name)
         except OSError:

nvcurve/profiles/apply.py

@@ -43,7 +43,8 @@ def apply_profile(gpu_index: int, name: str, cfg) -> list[str]:
             errs.append(f"Mem offset: {msg}")
 
     if profile.power_limit_w is not None:
-        ok, msg = set_power_limit(profile.power_limit_w, gpu_index)
+        mode = profile.power_cap_mode or "nvml"
+        ok, msg = set_power_limit(profile.power_limit_w, gpu_index, mode)
         if not ok:
             errs.append(f"Power limit: {msg}")
 

nvcurve/profiles/native.py

@@ -16,6 +16,9 @@ class ProfileData:
     curve_deltas: dict[str, int]  # { "index": delta_khz }
     mem_offset_mhz: int | None = None
     power_limit_w: int | None = None
+    # How power_limit_w is applied: "nvml" (default) or "ioctl" (experimental
+    # RM power control, permits values below the VBIOS minimum).
+    power_cap_mode: str | None = None
     fan_curve: list[dict[str, int]] | None = None
     # Fan indices controlled by fan_curve (0-based); None = all fans.
     fan_targets: list[int] | None = None
@@ -55,6 +58,9 @@ def load_profile(filepath: str) -> ProfileData:
     # Drop removed fields so old profiles don't cause TypeError.
     for obsolete in ("gpu_locked_min_mhz", "gpu_locked_max_mhz", "vram_p0_offset_mhz"):
         data.pop(obsolete, None)
+    # Normalize the experimental power-cap mode; unknown values fall back to NVML.
+    if data.get("power_cap_mode") not in (None, "nvml", "ioctl"):
+        data["power_cap_mode"] = None
     return ProfileData(**data)
 
 

nvcurve/server.py

@@ -569,6 +569,8 @@ class SnapshotRestoreRequest(BaseModel):
 class LimitsRequest(BaseModel):
     power_limit_w: int | None = None
     mem_offset_mhz: int | None = None
+    # "nvml" (default) or "ioctl" (experimental RM power control).
+    power_cap_mode: str | None = None
 
 
 class ProfileSaveRequest(BaseModel):
@@ -914,6 +916,17 @@ def _persist_fan_curves(fan_curves: dict) -> None:
     _persist_config_field("fan_curves", fan_curves if fan_curves else None)
 
 
+def _persist_power_cap_modes(modes: dict[str, str]) -> None:
+    """Persist the per-GPU experimental power-cap mode dict to config.json."""
+    _persist_config_field("power_cap_modes", modes if modes else None)
+
+
+def _power_cap_mode(cfg: Config, gpu_index: int) -> str:
+    """Return the effective power-cap mode for a GPU ("nvml" or "ioctl")."""
+    mode = cfg.power_cap_modes.get(_gpu_stable_key(gpu_index), "nvml")
+    return mode if mode in ("nvml", "ioctl") else "nvml"
+
+
 @app.get("/api/profiles")
 async def api_profiles(gpu_index: int = 0):
     """List saved native profiles, the active profile name, and the auto-load profile name."""
@@ -941,13 +954,15 @@ async def api_profile_save(req: ProfileSaveRequest, gpu_index: int = 0):
     curve_deltas = {str(p.index): p.delta_khz for p in state.points if p.delta_khz != 0}
 
     try:
-        power_info = await _run(get_power_limit, gpu_index)
+        mode = _power_cap_mode(cfg, gpu_index)
+        power_info = await _run(get_power_limit, gpu_index, mode)
         offsets = await _run(get_clock_offsets, gpu_index)
         power_limit_w = power_info.get("power_limit_w")
         mem_offset_mhz = offsets.get("mem_offset_mhz")
     except Exception:
         power_limit_w = None
         mem_offset_mhz = None
+        mode = "nvml"
 
     data = ProfileData(
         name=req.name,
@@ -955,6 +970,7 @@ async def api_profile_save(req: ProfileSaveRequest, gpu_index: int = 0):
         curve_deltas=curve_deltas,
         mem_offset_mhz=mem_offset_mhz,
         power_limit_w=power_limit_w,
+        power_cap_mode=mode,
         fan_curve=g_state.get("fan_curve") if g_state.get("fan_curve_active") else None,
         fan_targets=g_state.get("fan_targets")
         if g_state.get("fan_curve_active")
@@ -1075,7 +1091,8 @@ async def _apply_profile(name: str, gpu_index: int = 0) -> list[str]:
             errs.append(f"Mem offset: {msg}")
 
     if profile.power_limit_w is not None:
-        ok, msg = await _run(set_power_limit, profile.power_limit_w, gpu_index)
+        mode = profile.power_cap_mode or "nvml"
+        ok, msg = await _run(set_power_limit, profile.power_limit_w, gpu_index, mode)
         if not ok:
             errs.append(f"Power limit: {msg}")
 
@@ -1204,7 +1221,9 @@ async def api_config_update(req: ConfigUpdateRequest):
 @app.get("/api/limits")
 async def api_limits(gpu_index: int = 0):
     """Current performance limits: power and clock offsets."""
-    power = await _run(get_power_limit, gpu_index)
+    cfg: Config = _state["config"]
+    mode = _power_cap_mode(cfg, gpu_index)
+    power = await _run(get_power_limit, gpu_index, mode)
     offsets = await _run(get_clock_offsets, gpu_index)
     mem_off_range = await _run(get_mem_offset_range, gpu_index)
     return {
@@ -1218,10 +1237,36 @@ async def api_limits(gpu_index: int = 0):
 async def api_limits_update(req: LimitsRequest, gpu_index: int = 0):
     """Update performance limits."""
     g_state = _get_gpu_state(gpu_index)
+    cfg: Config = _state["config"]
     errs = []
 
+    if req.power_cap_mode is not None:
+        if req.power_cap_mode not in ("nvml", "ioctl"):
+            raise HTTPException(
+                status_code=400, detail="power_cap_mode must be 'nvml' or 'ioctl'"
+            )
+        if req.power_cap_mode == "ioctl":
+            # Verify the GPU actually exposes the RM interface before enabling,
+            # so a client can't lock a GPU into a mode where every power
+            # operation fails (ioctl mode has no NVML fallback by design).
+            info = await _run(get_power_limit, gpu_index, "ioctl")
+            if not info.get("rm_power_supported"):
+                raise HTTPException(
+                    status_code=409,
+                    detail="Experimental RM power control is not supported "
+                    "on this GPU/driver",
+                )
+        key = _gpu_stable_key(gpu_index)
+        if req.power_cap_mode == "nvml":
+            cfg.power_cap_modes.pop(key, None)
+        else:
+            cfg.power_cap_modes[key] = "ioctl"
+        _persist_power_cap_modes(cfg.power_cap_modes)
+
+    mode = _power_cap_mode(cfg, gpu_index)
+
     if req.power_limit_w is not None:
-        ok, msg = await _run(set_power_limit, req.power_limit_w, gpu_index)
+        ok, msg = await _run(set_power_limit, req.power_limit_w, gpu_index, mode)
         if not ok:
             errs.append(f"Power Limit: {msg}")
 
@@ -1284,12 +1329,17 @@ async def _update_offsets_and_broadcast(gpu_index: int) -> None:
 async def api_limits_reset(gpu_index: int = 0):
     """Reset power limit to hardware default and memory clock offset to 0."""
     g_state = _get_gpu_state(gpu_index)
+    cfg: Config = _state["config"]
     errs = []
 
-    power = await _run(get_power_limit, gpu_index)
+    # Reset uses the GPU's current mode: in ioctl mode the default is
+    # restored through the RM route (which can also restore a previous
+    # below-VBIOS-minimum cap).
+    mode = _power_cap_mode(cfg, gpu_index)
+    power = await _run(get_power_limit, gpu_index, mode)
     default_w = power.get("default_power_limit_w")
     if default_w is not None:
-        ok, msg = await _run(set_power_limit, default_w, gpu_index)
+        ok, msg = await _run(set_power_limit, default_w, gpu_index, mode)
         if not ok:
             errs.append(f"Power Limit: {msg}")