linux-kernel - Re: [PATCH v8 05/10] dt-bindings: i3c: Add macros to help fill I3C/I2C device's reg property

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Date:   Wed, 3 Oct 2018 20:59:53 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Joe Perches <joe@...ches.com>, Rob Herring <robh+dt@...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@...tlin.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, Sekhar Nori <nsekhar@...com>,
        Przemyslaw Gaj <pgaj@...ence.com>,
        Peter Rosin <peda@...ntia.se>,
        Mike Shettel <mshettel@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH v8 05/10] dt-bindings: i3c: Add macros to help fill
 I3C/I2C device's reg property

On Wed, 03 Oct 2018 11:37:17 -0700
Joe Perches <joe@...ches.com> wrote:

> On Wed, 2018-10-03 at 15:22 +0200, Boris Brezillon wrote:
> > The reg property of devices connected to an I3C bus have 3 cells, and
> > filling them manually is not trivial. Provides macros to help doing
> > that.  
> 
> This patch logic seems excessively fragile.

Keep in mind that this header is meant to be include by .dts(i) files,
not regular .c files.

> 
> > Signed-off-by: Boris Brezillon <boris.brezillon@...tlin.com>
> > Reviewed-by: Rob Herring <robh@...nel.org>
> > ---
> > Changes in v8:
> > - None
> > 
> > Changes in v5:
> > - none
> > ---
> >  include/dt-bindings/i3c/i3c.h | 28 ++++++++++++++++++++++++++++
> >  1 file changed, 28 insertions(+)
> >  create mode 100644 include/dt-bindings/i3c/i3c.h
> > 
> > diff --git a/include/dt-bindings/i3c/i3c.h b/include/dt-bindings/i3c/i3c.h
> > new file mode 100644
> > index 000000000000..97448c546649
> > --- /dev/null
> > +++ b/include/dt-bindings/i3c/i3c.h
> > @@ -0,0 +1,28 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2017 Cadence Design Systems Inc.
> > + *
> > + * Author: Boris Brezillon <boris.brezillon@...tlin.com>
> > + */
> > +
> > +#ifndef _DT_BINDINGS_I3C_I3C_H
> > +#define _DT_BINDINGS_I3C_I3C_H
> > +
> > +#define IS_I2C_DEV		0x80000000
> > +
> > +#define I2C_DEV(addr, lvr)					\
> > +	(addr) (IS_I2C_DEV | (lvr)) 0x0  
> 
> This looks to be missing surrounding parentheses.

Actually it's not. The macro is supposed to declare 3 u32 integers each
of them separated by a space:

	reg = <I2C_DEV(0x34, 0x1)>;

is translated into

	reg = <0x34 0x80000001 0x0>;

> 
> > +
> > +#define I3C_PID(manufid, partid, instid, extrainfo)		\
> > +	((manufid) << 1)					\
> > +	(((partid) << 16) | ((instid) << 12) | (extrainfo))  
> 
> This macro doesn't make any sense.  Missing a shift and an or?

Same here, the PID is taking 2 32-bit entries.

Now, I agree that this is far from obvious, and if Rob is okay, I'd
like to propose a different binding to avoid having to define these
macros:

	reg = <i2c_addr_or_i3c_static_addr pid_msb pid_lsb>;

If pid_msb and pid_lsb are 0, then the node is defining an I2C device
(AFAICT, 0 is not a valid PID), otherwise it's an I3C device. This way
we get rid of the IS_I2C_DEV flag, and we can get rid of those macros
without making I3C dev node definition too painful (the only part
developers will have to get right is the PID) 

> 
> > +
> > +#define I3C_DEV_WITH_STATIC_ADDR(addr, manufid, partid,		\
> > +				 instid, extrainfo)		\
> > +	(addr) I3C_PID(manufid, partid, instid, extrainfo)
> > +
> > +#define I3C_DEV(manufid, partid, instid, extrainfo)		\
> > +	I3C_DEV_WITH_STATIC_ADDR(0x0, manufid, partid,		\
> > +				 instid, extrainfo)
> > +
> > +#endif  
>