Hi, I just watched the amazing device tree presentation recently done by Thomas Petazzoni (from Bootlin) for ST[1]. During the presentation, which is amazing, by the way ;-), Thomas describes the 1-wire protocol as not being discoverable. I was recently playing with the DS18B20 temperature sensor, which uses the 1-wire bus.[2] In fact, I was playing with a bunch of different temperature sensors with a RaspberryPi, and then gave a talk at a local RaspberryPi Meetup group that I regularly attend.[3] My only experience with the 1-wire bus is with this one device, so maybe the details of how the DS18B20 work are specific to the DS18B20 and not the way 1-wire devices work in general? But my (humble) conclusion is that the 1-wire bus is discoverable (or at least quasi-discoverable). It's true that you do need a device tree overlay to tell the kernel that you want to use the 1-wire bus, and you have to tell the kernel which GPIO pin you want to use as the 1 wire, but after that, attaching DS18B20 devices to a running system works quite magically.[4] Each DS18B20 has a unique 64-bit number burned into it, the first 8 bits specify the device type (i.e. the DS18B20), the next 48 bits are a unique serial number, and the last 8 bits are a CRC of the previous 56 bits. Due to the inclusion of the 8-bit device type, when I plug a DS18B20 into my board, the kernel automatically creates a sysfs entry for it with a "temperature" file that I can read to obtain the temperature in Celcius. I don't know if that qualifies as "discoverable"? It's certainly a lot more discoverable than I2C or SPI, although maybe not quite as discoverable as, say, PCI. Specifying the 1 wire is not discoverable, but plugging 1-wire devices into my board is maybe something that could be described as discoverable? Best regards, Trevor [1] https://www.youtube.com/watch?v=a9CZ1Uk3OYQ [2] https://twoerner.blogspot.com/2020/12/temperature-readings-with-ds18b20-and.html [3] https://twoerner.blogspot.com/2021/01/sensing-temperature-with-raspberrypi.html [4] https://twoerner.blogspot.com/2020/12/multiple-ds18b20-temperature-probes.html _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
