[RESEND PATCH 5/5] Documentation: wmi: bitland-mifs-wmi: document MIFS v2 firmware variant

["孙 誉铭" <wolf109909@outlook.com>]

Document the reduced MIFS v2 command set found on newer machines:
QFAN performance-mode codes {2,3,4,9,10}, fan tachometer location in
the EC shared-memory window (no WMI fan function), the missing ECON
definition that disables the ACPI EC driver (and how the driver works
around it for the lid switch), and the WMAA reply status word.

Signed-off-by: Yuming Sun <wolf109909@outlook.com>
---
 .../wmi/devices/bitland-mifs-wmi.rst          | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Documentation/wmi/devices/bitland-mifs-wmi.rst b/Documentation/wmi/devices/bitland-mifs-wmi.rst
index 9e86ecc2..d019a4c8 100644
--- a/Documentation/wmi/devices/bitland-mifs-wmi.rst
+++ b/Documentation/wmi/devices/bitland-mifs-wmi.rst
@@ -133,6 +133,32 @@ The driver listens for events from the ``HID_EVENT20`` class
 (GUID: ``{46c93e13-ee9b-4262-8488-563bca757fef}``). These events are triggered
 by hotkeys or system state changes (e.g., plugging in AC power).
 
+MIFS v2 firmware variant
+========================
+
+Some newer machines (e.g. Xiaomi Book Pro 14 2026, REDMI Book Pro 14 2025)
+ship a reduced MIFS firmware, called "v2" here. Its WMAA method implements
+only function groups 0x0800/0x0a00/0x0c00/0x1000, so of the command table
+above only SystemPerMode (0x08) and a few state toggles exist. Differences:
+
+* SystemPerMode (0x08) reports raw QFAN EC codes instead of the 0..3
+  enumeration: 2 = Quiet, 3 = Balanced, 4 = Speed, 9/10 = Extreme
+  (SMM-backed). The driver maps these to platform profiles and detects the
+  variant at probe time when the reported mode is outside the v1 range.
+* There is no WMI fan-speed or CPU-temperature function. The two fan
+  tachometers live in the EC shared-memory window at 0xFE0B0300 (DSDT
+  \_SB.PC00.LPCB.Q_EC region "ERAM") as little-endian u16 RPM values at
+  offsets 0x69 and 0x6B (0 = fan stopped). The EC controls the fans
+  autonomously; no OS fan-speed override exists on this firmware.
+* The firmware never defines ECON, so \_SB.PC00.LPCB.Q_EC._STA fails, the
+  ACPI EC driver never binds and EC query handlers (lid switch _Q0C/_Q0D,
+  hotkey queries) never run. On DMI-matched models the driver polls the
+  LSTE lid bit (offset 0x14, bit 0) in the EC window and evaluates
+  _Q0C/_Q0D itself so the PNP0C0D lid device keeps emitting SW_LID.
+* The reply status word (bytes 0-1 of OutData, SGER) is 0x8000 on success
+  and 0xe000 for unknown/unsupported functions; the driver turns the
+  latter into -EOPNOTSUPP.
+
 Event Structure
 ---------------
 
-- 
2.55.0