hwmon: Add Minisforum UM780 XTX EC monitoring and fan control

Add a DMI-gated hwmon driver for the embedded controller used by the
Minisforum UM780 XTX with board revision 1.1 and BIOS 1.06.

Expose the CPU and system fan control temperatures and tachometers. The
tachometer protocol returns one byte per OEM command, so serialize
transactions and use high-low-high sampling to reject torn values.

Allow selecting either complete OEM CPU fan profile through pwm1_enable and
changing the two validated system fan transition temperatures through
standard automatic-curve attributes. Cache coherent settings and restore
them after the firmware reloads defaults following resume.

Signed-off-by: Sebastián Peyrott <speyrott@gmail.com>
Link: https://patch.msgid.link/20260902000509.191115-1-speyrott@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

2 files changed, 69 insertions, 0 deletions

diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
index 06a7992ce5da..f07977a20271 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -187,6 +187,7 @@ Hardware Monitoring Kernel Drivers
    mcp3021
    mcp9982
    menf21bmc
+   minisforum-um780xtx
    mlxreg-fan
    mp2856
    mp2869
diff --git a/Documentation/hwmon/minisforum-um780xtx.rst b/Documentation/hwmon/minisforum-um780xtx.rst
new file mode 100644
index 000000000000..8237d525a9c7
--- /dev/null
+++ b/Documentation/hwmon/minisforum-um780xtx.rst
@@ -0,0 +1,68 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+====================================
+Kernel driver minisforum-um780xtx
+====================================
+
+Supported systems:
+
+  * Minisforum UM780 XTX
+
+    * DMI product name: ``Venus series``
+    * Mainboard: ``F7BSD``, revision ``1.1``
+    * BIOS version: ``1.06``
+
+Author: Sebastián Peyrott <speyrott@gmail.com>
+
+Description
+-----------
+
+This driver exposes hardware monitoring and fan-control data cached by the
+IT5571E embedded controller. It uses the ACPI EC transport and only binds to
+the exact system and firmware identity listed above.
+
+The two temperature channels are the values used by the EC's fan-control
+loops. Their physical sensor placement is not known. The CPU channel is the
+filtered AMD SB-TSI temperature, while the system channel is an external
+thermistor input.
+
+The fan tachometers are read through OEM EC commands. Since each byte is
+returned by a separate command, the driver uses a high-low-high sequence and
+retries if the high byte changes.
+
+Sysfs entries
+-------------
+
+==========================  ==============================================
+``temp1_input``             CPU-fan control temperature
+``temp2_input``             System-fan control temperature
+``fan1_input``              CPU fan speed in RPM
+``fan2_input``              System fan speed in RPM
+``pwm1_enable``             CPU profile: 2 is OEM B1, 3 is OEM B2
+``pwm2_auto_point1_temp``   Off-to-low system-fan transition temperature
+``pwm2_auto_point2_temp``   Low-to-high system-fan transition temperature
+==========================  ==============================================
+
+CPU fan profiles
+----------------
+
+Values 2 and 3 of ``pwm1_enable`` select the two complete automatic profiles
+implemented by the firmware. Writing either value reloads the whole CPU fan
+curve, including firmware state which is not visible through the ACPI EC
+window. Other values are rejected.
+
+System fan thresholds
+---------------------
+
+The two writable system-fan temperatures are rounded to whole degrees Celsius
+and clamped to preserve strict ordering between both visible thresholds and
+the firmware's internal third threshold. The third threshold does not select
+a new PWM target and is therefore not exposed as another auto point.
+
+Resume state preservation
+-------------------------
+
+Fan settings are held in EC RAM. On the supported firmware, initialization
+during s2idle resume reloads the factory system-fan curve. The driver retains
+the last coherent CPU profile and system-fan thresholds selected through its
+interface and restores them synchronously at resume.