From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grant Likely Subject: Re: Device naming based on device tree Date: Sat, 13 Apr 2013 13:48:38 +0100 Message-ID: <20130413124838.EADC63E2249@localhost> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: "devicetree-discuss" To: Thomas De Schampheleire , devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Cc: Ronny Meeus List-Id: devicetree@vger.kernel.org On Mon, 21 Jan 2013 11:25:26 +0100, Thomas De Schampheleire wrote: > Hi, > > I'm trying to find a proper way for userspace to determine which > devices to talk to. Say you have 4 SPI devices that are registered > against spidev (the userspace SPI handling driver). The device tree > obviously knows which device is which (e.g. a temperature sensor, a > memory device, an actuator, ...) but userspace does not. In the case > of SPI, it sees things like: > /sys/class/spidev/spidev32766.1/ > or worse > /sys/devices/ffe000000.soc/ffe110000.spi/spi32766.1 > but these are too specific. > > The same problem occurs for devices using i2c-dev, uio, mtd, ... > > For uio, it's possible to determine which device i (i.e. the userspace > program needs to know that a) the device is an SPI devices which by > checking the /sys/class/uio/uioX/name files. > For mtd it is possible to do something similar by strategically > choosing the mtd partition descriptions and creating device nodes or > links based on that information. > > Basically, I'm looking for a way to give device tree nodes a name, so > that I can easily access or create devices like /dev/tempsensor0, > /dev/actuator, /dev/serialnum_memory, etc. Ideally such a mechanism is > bus-agnostic: on one board the temperature sensor may be using SPI, on > another I2C. > > I assume this is what udev is for, but I'm not sure if it fixes my > problem. In order to name/rename devices with udev, there need to be > rules, and these rules are part of userspace, I cannot dictate them > from the device tree. In an embedded world, you may have three boards > with the same userspace but with different hardware configurations and > thus different device trees. Yes, every time a new device is added to /sys/devices, a uevent will be issued that lets udev know that a new device is ready to be handled. The data associated with the uevent is exported via the 'uevent' attribute in the new device. The uevent attribute should have enough information to identify which dt node is associated with the device. Check the OF_FULLNAME value in uevent, and also the OF_ALIAS_* values. g.