Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752936AbdLUKmA (ORCPT ); Thu, 21 Dec 2017 05:42:00 -0500 Received: from mail.free-electrons.com ([62.4.15.54]:48976 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751822AbdLUKl5 (ORCPT ); Thu, 21 Dec 2017 05:41:57 -0500 Date: Thu, 21 Dec 2017 11:41:44 +0100 From: Boris Brezillon To: Rob Herring Cc: Wolfram Sang , linux-i2c@vger.kernel.org, Jonathan Corbet , linux-doc@vger.kernel.org, Greg Kroah-Hartman , Arnd Bergmann , Przemyslaw Sroka , Arkadiusz Golec , Alan Douglas , Bartosz Folta , Damian Kos , Alicja Jurasik-Urbaniak , Cyprian Wronka , Suresh Punnoose , Thomas Petazzoni , Nishanth Menon , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Vitor Soares , Geert Uytterhoeven , Linus Walleij Subject: Re: [PATCH v2 5/7] dt-bindings: i3c: Document core bindings Message-ID: <20171221114144.2610d49b@bbrezillon> In-Reply-To: <20171220180645.pis34opfwawakmqc@rob-hp-laptop> References: <20171214151610.19153-1-boris.brezillon@free-electrons.com> <20171214151610.19153-6-boris.brezillon@free-electrons.com> <20171216172040.jcaezouqkeb7zrqy@rob-hp-laptop> <20171216193537.0aef2e97@bbrezillon> <20171220180645.pis34opfwawakmqc@rob-hp-laptop> X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5823 Lines: 132 On Wed, 20 Dec 2017 12:06:45 -0600 Rob Herring wrote: > On Sat, Dec 16, 2017 at 07:35:37PM +0100, Boris Brezillon wrote: > > On Sat, 16 Dec 2017 11:20:40 -0600 > > Rob Herring wrote: > > > > > On Thu, Dec 14, 2017 at 04:16:08PM +0100, Boris Brezillon wrote: > > > > A new I3C subsystem has been added and a generic description has been > > > > created to represent the I3C bus and the devices connected on it. > > > > > > > > Document this generic representation. > > [...] > > > > So please define the node > > > name to be "i3c-controller". That's more inline with other node names > > > than i3c-master that you used below. > > > > Hm, not sure i3c-controller is appropriate though, because you can have > > slave controllers. Maybe i3c-host, but I'd prefer to keep the term > > master since it's employed everywhere in the spec. I can also be > > i3c-master-controller if you prefer. > > Okay, i3c-master is fine. Just make it explicit. Okay. > > > > > +I3C devices > > > > +=========== > > > > + > > > > +All I3C devices are supposed to support DAA (Dynamic Address Assignment), and > > > > +are thus discoverable. So, by default, I3C devices do not have to be described > > > > +in the device tree. > > > > +This being said, one might want to attach extra resources to these devices, > > > > +and those resources may have to be described in the device tree, which in turn > > > > +means we have to describe I3C devices. > > > > + > > > > +Another use case for describing an I3C device in the device tree is when this > > > > +I3C device has a static address and we want to assign it a specific dynamic > > > > +address before the DAA takes place (so that other devices on the bus can't > > > > +take this dynamic address). > > > > + > > > > +Required properties > > > > +------------------- > > > > +- i3c-pid: PID (Provisional ID). 64-bit property which is used to match a > > > > + device discovered during DAA with its device tree definition. The > > > > + PID is supposed to be unique on a given bus, which guarantees a 1:1 > > > > + match. This property becomes optional if a reg property is defined, > > > > + meaning that the device has a static address. > > > > > > What determines this number? > > > > Part of it is fixed (manufacturer and part id) and the last few bits > > represent the device instance on the bus (so you can have several > > identical devices on the same bus). The manufacturer and part ids > > should be statically assigned during production, instance id is usually > > configurable through extra pins that you drive high or low at reset > > time. > > Sounds like an I2C address at least for the pin strapping part... The address space of this instance-id is smaller (4bits) than the I2C one (7bits), and more importantly, the instance-id is not required to be unique, it's the aggregation of the vendor-id, part-id and instance-id that has to be unique. So, if you were thinking about using this id to uniquely identify the device on the bus it's not a good idea. > > > > > + > > > > +Optional properties > > > > +------------------- > > > > +- reg: static address. Only valid is the device has a static address. > > > > +- i3c-dynamic-address: dynamic address to be assigned to this device. This > > > > + property depends on the reg property. > > > > > > Perhaps "assigned-address" property would be appropriate. I'm not all > > > that familiar with it though. > > > > Again, the spec use the term "dynamic address" everywhere, and I'd like > > to stay as close as possible to the spec. > > I looked at assigned-addresses a bit more and that won't really fit > because it should be the same format as reg. So I think reg should > always be the PID as that is fixed and always present. Then the DAA > address is separate and can be the i3c-dynamic-address property. > > However, there's still part I don't understand... > > > > > + /* I3C device with a static address. */ > > > > + thermal_sensor: sensor@68 { > > > > + reg = <0x68>; > > > > + i3c-dynamic-address = <0xa>; > > I'm confused as to how/why you have both reg and dynamic address? Some I3C devices have an I2C address (also called static or legacy address in a few places). The static/I2C/legacy address is used until the I3C device is assigned a dynamic address by the master. The whole point of specifying both an I2C address (through the reg property) and a dynamic address (through the i3c-dynamic-address) is to tell the controller that a specific dynamic address should be assigned to this device using the SETSADA (Set Dynamic Address from Static Address) command before a DAA (Dynamic Address Assignment) procedure is started. This way, the device will not participate to the DAA (because it already has a valid DA) and the dynamic address can't be assigned to a different device (which is one of the problem with the automatic DAA procedure). > > > > > + }; > > > > + > > > > + /* > > > > + * I3C device without a static address but requiring resources > > > > + * described in the DT. > > > > + */ > > > > + sensor2 { > > > > > > It's not great that we can't follow using generic node names. Maybe the > > > PID can be used as the address? In USB for example, we use hub ports for > > > DT addresses rather than USB addresses since those are dynamic. > > > > Hm, the problem is, we may have 2 numbering schemes here: one where reg > > is used (reg representing the I2C/static address), and another one > > where the PID is used. > > If you're okay with mixing those 2 schemes, then I'm fine with that too. > > Mixing I2C devices and I3C devices, yes. But you need to mix in a single > device? IOW, do I3C devices also have an I2C address? Yes, some of them have both.