linux-kernel - Re: [PATCH v4 2/8] i2c: add I2C Address Translator (ATR) support

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Date:   Mon, 7 Nov 2022 12:40:55 +0100
From:   Luca Ceresoli <luca.ceresoli@...tlin.com>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...el.com>,
        devicetree@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Luca Ceresoli <luca@...aceresoli.net>,
        Mark Rutland <mark.rutland@....com>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Peter Rosin <peda@...ntia.se>,
        Rob Herring <robh+dt@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        satish.nagireddy@...cruise.com
Subject: Re: [PATCH v4 2/8] i2c: add I2C Address Translator (ATR) support

On Fri, 4 Nov 2022 13:59:06 +0200
Tomi Valkeinen <tomi.valkeinen@...asonboard.com> wrote:

> Hi Andy,
> 
> On 01/11/2022 16:30, Andy Shevchenko wrote:
> > On Tue, Nov 01, 2022 at 03:20:26PM +0200, Tomi Valkeinen wrote:  
> >> From: Luca Ceresoli <luca@...aceresoli.net>
> >>
> >> An ATR is a device that looks similar to an i2c-mux: it has an I2C
> >> slave "upstream" port and N master "downstream" ports, and forwards
> >> transactions from upstream to the appropriate downstream port. But is
> >> is different in that the forwarded transaction has a different slave
> >> address. The address used on the upstream bus is called the "alias"
> >> and is (potentially) different from the physical slave address of the
> >> downstream chip.
> >>
> >> Add a helper file (just like i2c-mux.c for a mux or switch) to allow
> >> implementing ATR features in a device driver. The helper takes care or
> >> adapter creation/destruction and translates addresses at each transaction.  

First of all, thank you for bringing this work on!

> > ...
> >   
> >> +I2C ADDRESS TRANSLATOR (ATR)
> >> +M:	Luca Ceresoli <luca@...aceresoli.net>  
> > 
> > Hmm... Are you going to maintain this? Or Review? Why not?  
> 
> We haven't discussed with Luca if he wants to maintain this (this is 
> mostly his code). But, indeed, I should add my name there.

I think at this point you are probably in a better position to be the
maintainer, but I'm OK with being listed here as reviewer (R:).

Ah, would you please use my bootlin dot com address here?

> I'm not arguing against any of the comments you've made, I think they 
> are all valid, but I want to point out that many of them are in a code 
> copied from i2c-mux.
> 
> Whether there's any value in keeping i2c-mux and i2c-atr similar in 
> design/style... Maybe not.

Tomi is right, when I wrote this initially I tried to keep it as
similar as possible to i2c-mux.c. No problem in deviating from that
wherever it makes sense.

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com