Re: [PATCH RFC 3/4] hwmon: Add driver for Raspberry Pi RP1 fan tachometer

[Uwe Kleine-König]

Hello,

On Fri, Oct 23, 2026 at 12:15:56PM +0200, Andrea della Porta wrote:
> Add a hardware monitoring driver to support the fan tachometer on the
> Raspberry Pi RP1 southbridge, found on the Raspberry Pi 5.
> 
> The RP1 PWM controller block contains specific MMIO registers that hold
> the current fan speed in RPM. These registers are periodically updated by
> the RP1 internal firmware based on the tachometer pulses.
> 
> Since the Linux PWM subsystem does not currently offer a framework for
> exposing integrated hardware tachometer readings, this driver is
> implemented as a standalone hwmon device. It parses the
> 'raspberrypi,pwm-tachometer' DT property to find the supplier PWM device,
> establishes a device link to ensure proper lifecycle management, and uses
> RP1-specific PWM functions to retrieve the RPM values.

I wonder if the tachometer readout should be a counter driver? That
would allow this driver to not be specific to the RP1 hardware.

Best regards
Uwe

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