linux-kernel - Re: [PATCH v3 05/11] dt-bindings: i3c: Document core bindings

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Date:   Wed, 28 Mar 2018 10:19:22 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Przemyslaw Sroka <psroka@...ence.com>,
        Arkadiusz Golec <agolec@...ence.com>,
        Alan Douglas <adouglas@...ence.com>,
        Bartosz Folta <bfolta@...ence.com>,
        Damian Kos <dkos@...ence.com>,
        Alicja Jurasik-Urbaniak <alicja@...ence.com>,
        Cyprian Wronka <cwronka@...ence.com>,
        Suresh Punnoose <sureshp@...ence.com>,
        Rafal Ciepiela <rafalc@...ence.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Nishanth Menon <nm@...com>, Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vitor Soares <Vitor.Soares@...opsys.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Xiang Lin <Xiang.Lin@...aptics.com>,
        linux-gpio@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...e-electrons.com>
Subject: Re: [PATCH v3 05/11] dt-bindings: i3c: Document core bindings

Hi Rob,

On Mon, 26 Mar 2018 17:24:58 -0500
Rob Herring <robh@...nel.org> wrote:

> > +
> > +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  
> 
> static is I2C address and dynamic is an I3C address. That could be 
> clearer throughout.

I'll clarify that.

> 
> > +take this dynamic address).
> > +
> > +The I3C device should be names <device-type>@<static-address>,<i3c-pid>,  
> 
> s/static-address/static-i2c-address/

Okay.

> 
> > +where device-type is describing the type of device connected on the bus
> > +(gpio-controller, sensor, ...).
> > +
> > +Required properties
> > +-------------------
> > +- reg: contains 3 cells
> > +  + first cell : encodes the I2C address. Should be 0 if the device does not
> > +		 have one (0 is not a valid I3C address).  
> 
> Change here to "encodes the static I2C address". 
> 
> 0 is not a valid I2C address?

According to [1] it is reserved, and it's reserved in the I3C spec
anyway (see "Table 9 I3C Slave Address Restrictions" in the I3C spec).

> 
> > +
> > +  + second and third cells: should encode the ProvisionalID. The second cell
> > +			    contains the manufacturer ID left-shifted by 1.
> > +			    The third cell contains ORing of the part ID
> > +			    left-shifted by 16, the instance ID left-shifted
> > +			    by 12 and the extra information. This encoding is
> > +			    following the PID definition provided by the I3C
> > +			    specification.

One extra question for you: should I refer to the I3C_DEV(),
I3C_DEV_WITH_STATIC_ADDR() and I2C_DEV() macros in the bindings doc?
And if I do, should I use them my example?

Thanks,

Boris

> > +
> > +Optional properties
> > +-------------------
> > +- assigned-address: dynamic address to be assigned to this device. This
> > +		    property is only valid if the I3C device has a static
> > +		    address (first cell of the reg property != 0).
> > +
> > +
> > +Example:
> > +
> > +	i3c-master@...0000 {
> > +		compatible = "cdns,i3c-master";
> > +		clocks = <&coreclock>, <&i3csysclock>;
> > +		clock-names = "pclk", "sysclk";
> > +		interrupts = <3 0>;
> > +		reg = <0x0d040000 0x1000>;
> > +		#address-cells = <3>;
> > +		#size-cells = <0>;
> > +
> > +		status = "okay";
> > +		i2c-scl-frequency = <100000>;
> > +
> > +		/* I2C device. */
> > +		nunchuk: nunchuk@52 {
> > +			compatible = "nintendo,nunchuk";
> > +			reg = <0x52 0x80000010 0x0>;
> > +		};
> > +
> > +		/* I3C device with a static address. */
> > +		thermal_sensor: sensor@68,39200144004 {
> > +			reg = <0x68 0x392 0x144004>;
> > +			assigned-address = <0xa>;
> > +		};
> > +
> > +		/*
> > +		 * I3C device without a static address but requiring resources
> > +		 * described in the DT.
> > +		 */
> > +		sensor@0,39200154004 {
> > +			reg = <0x0 0x392 0x154004>;
> > +			clocks = <&clock_provider 0>;
> > +		};
> > +	};
> > +
> > -- 
> > 2.14.1
> >   

[1]http://www.i2c-bus.org/addressing

-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com