From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wolfram Sang <wsa@the-dreams.de>
Subject: Re: [RFC,v2 2/6] i2c: add I2C Address Translator (ATR) support
Date: Mon, 2 Sep 2019 22:42:08 +0200
Message-ID: <20190902204208.GA7253@kunai>
References: <20190723203723.11730-1-luca@lucaceresoli.net>
 <20190723203723.11730-3-luca@lucaceresoli.net>
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To: Luca Ceresoli <luca@lucaceresoli.net>
Cc: linux-media@vger.kernel.org, linux-i2c@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Mauro Carvalho Chehab <mchehab@kernel.org>, Rob Herring <robh+dt@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Sakari Ailus <sakari.ailus@linux.intel.com>, Hans Verkuil <hverkuil-cisco@xs4all.nl>, Laurent Pinchart <laurent.pinchart@ideasonboard.com>, Kieran Bingham <kieran.bingham@ideasonboard.com>, Jacopo Mondi <jacopo@jmondi.org>, Vladimir Zapolskiy <vz@mleia.com>, Peter Rosin <peda@axentia.se>
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Hi Luca,

> + * Topology:
> + *
> + *                       Slave X @ 0x10
> + *               .-----.   |
> + *   .-----.     |     |---+---- B
> + *   | CPU |--A--| ATR |
> + *   `-----'     |     |---+---- C
> + *               `-----'   |
> + *                       Slave Y @ 0x10
> + *
> + * Alias table:
> + *
> + *   Client  Alias
> + *   -------------
> + *      X    0x20
> + *      Y    0x30

Great that you already provided docs for this driver!

One huge drawback for me is the attach/detach callbacks. One year ago, I
removed a similar callback from the I2C core ("[PATCH 0/2] i2c: remove
deprecated attach_adapter callback") because some drivers did a lot of
crazy things there. It took years to remove all that.

What I could imagine here: the adapter (B and C each in the picture
above) gets a flag like NEEDS_ATR before registering to the core. The
flag means all clients on that bus will have their address translated.
The core will figure out a free alias when a device is registered. We
can then have an ATR specific callback with the original and translated
address as arguments, so one can setup the HW as needed.

Do you think that would work? Jacopo, does that meet GMSL as well?

Regards,

   Wolfram

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