arm64: enable CONFIG_PWM_RP1 for Raspberry Pi 5 fan control

[blacksd]

Problem

The Raspberry Pi 5 dedicated 4-pin PWM fan header does not work on Talos v1.12.6 (kernel 6.18.18-talos). The fan never spins, causing thermal issues.

Kernel log:

platform cooling_fan: deferred probe pending: pwm-fan: Could not get PWM

Root Cause

The arm64 kernel config is missing the RP1 PWM drivers needed for the Pi 5 southbridge fan controller:

# Not present in config-arm64:
CONFIG_PWM_RP1=y
CONFIG_PWM_PIO_RP1=y

The cooling_fan device is defined in the Pi 5 device tree and requires the RP1 PWM driver to acquire a PWM channel. Without it, the fan probe is permanently deferred.

Current /proc/config.gz on v1.12.6 shows only:

CONFIG_PWM_GPIO=y
CONFIG_PWM_RASPBERRYPI_POE=y

Prior Art

PR #1375 enabled CONFIG_SENSORS_GPIO_FAN and CONFIG_PWM_GPIO for GPIO-connected fans (RPi 4), but did not address the Pi 5's native fan header which depends on the RP1 PWM driver.

The community talos-rpi5 custom builder (https://github.com/talos-rpi5/talos-builder) has been shipping these kernel configs to work around this.

Suggested Fix

Add to kernel/build/config-arm64:

CONFIG_PWM_RP1=y
CONFIG_PWM_PIO_RP1=y

These are in-tree drivers (not out-of-tree patches) in recent kernel versions.

Environment

• Talos v1.12.6 (arm64), kernel 6.18.18-talos
• Raspberry Pi 5 with dedicated 4-pin PWM fan (52Pi Armor case)
• SBC overlay: sbc-raspberrypi:v0.2.0, name: rpi_5