linux-kernel - Re: [PATCH v5 02/10] docs: driver-api: Add I3C documentation

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Date:   Wed, 27 Jun 2018 09:20:36 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Randy Dunlap <rdunlap@...radead.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>, Rob Herring <robh+dt@...nel.org>,
        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>
Subject: Re: [PATCH v5 02/10] docs: driver-api: Add I3C documentation

Hi Randy,

On Tue, 26 Jun 2018 14:07:49 -0700
Randy Dunlap <rdunlap@...radead.org> wrote:


> > +
> > +I3C Private SDR transfers
> > +-------------------------
> > +
> > +Private SDR (Single Data Rate) transfers should be used for anything that is
> > +device specific and does not require high transfer speed.
> > +
> > +It is the equivalent of I2C transfers but in the I3C world. Each transfer is
> > +passed the device address (dynamic address assigned during DAA), a payload
> > +and a direction.
> > +
> > +The only difference with I2C is that the transfer is much faster (typical SCL  
> 
> what is SCL?  It's not used anywhere else in this doc.

It's an acronym used by I²C, it means Serial Clock Line. I'll just
replace that by "typical clock frequency is 12.5MHz".

> 
> > +frequency is 12.5MHz).
> > +
> > +I3C HDR commands
> > +----------------
> > +
> > +HDR commands should be used for anything that is device specific and requires
> > +high transfer speed.
> > +
> > +The first thing attached to an HDR command is the HDR mode. There are currently
> > +3 different modes defined by the I3C specification (refer to the specification
> > +for more details):
> > +
> > +* HDR-DDR: Double Data Rate mode
> > +* HDR-TSP: Ternary Symbol Pure. Only usable on busses with no I2C devices
> > +* HDR-TSL: Ternary Symbol Legacy. Usable on busses with I2C devices
> > +
> > +When sending an HDR command, the whole bus has to enter HDR mode, which is done
> > +using a broadcast CCC command.
> > +Once the bus has entered a specific HDR mode, the master sends the HDR command.
> > +An HDR command is made of:
> > +
> > +* one 16-bits command word
> > +* N 16-bits data words  
> 
> I supposed the I3C spec will tell me the byte order of these words on the bus?
> or this doc could tell us here.

It's big endian. I'll make it clear in this doc.

I'll also fix all the other mistakes you pointed out.

> 
> and you can add (if you want to):
> Reviewed-by: Randy Dunlap <rdunlap@...radead.org>

I'll definitely add your R-b. Thanks for the review.

Boris