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Tue, 27 Oct 2026 10:32:46 -0700 (PDT) Received: from localhost ([82.192.120.214]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a92b881f90sm5173585e9.11.2026.10.27.10.32.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Oct 2026 10:32:45 -0700 (PDT) From: Andrea della Porta X-Google-Original-From: Andrea della Porta Date: Tue, 27 Oct 2026 18:36:37 +0100 To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: Andrea della Porta , Guenter Roeck , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Florian Fainelli , Broadcom internal kernel review list , Jonathan Corbet , Shuah Khan , Randy Dunlap , Laurent Pinchart , Gregor Herburger , Stanimir Varbanov , linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-pwm@vger.kernel.org, Gary Guo , Christophe JAILLET Subject: Re: [PATCH RFC 3/4] hwmon: Add driver for Raspberry Pi RP1 fan tachometer Message-ID: References: <0d2249a66732bfce38a2260bee08cd1ba4097e51.1792748690.git.andrea.porta@suse.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Hi Uwe, On 17:32 Tue 27 Oct , Uwe Kleine-König wrote: > 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. I suspect the counter driver won't work with userspace daemons (e.g. fancontrol) which use hwmon as an interface. OTOH this driver is indeed specific to the RP1 driver: the fan rpm are read from the same registers range and hw of teh PWM controller. Regards, Andrea > > Best regards > Uwe