linux-kernel - Re: [RFC 2/5] i3c: Add core I3C infrastructure

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Message-ID: <1538596b-80ed-7800-db97-70e73b90b9e2@ti.com>
Date:   Tue, 1 Aug 2017 11:47:15 -0500
From:   "Andrew F. Davis" <afd@...com>
To:     Wolfram Sang <wsa@...-dreams.de>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>
CC:     Arnd Bergmann <arnd@...db.de>, <linux-i2c@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>, <linux-doc@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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>,
        Jan Kotas <jank@...ence.com>,
        Cyprian Wronka <cwronka@...ence.com>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.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 Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 2/5] i3c: Add core I3C infrastructure

On 07/31/2017 04:42 PM, Wolfram Sang wrote:
> 
>> Actually, that's the first option I considered, but I3C and I2C are
>> really different. I'm not talking about the physical layer here, but
>> the way the bus has to be handled by the software layer. Actually, I
>> thing the I3C bus is philosophically closer to auto-discoverable busses
>> like USB than I2C or SPI.
> 
> Acked-by: Wolfram Sang <wsa@...-dreams.de>
> 
>> Of course, I can move all the code in drivers/i2c/, but that won't
>> change the fact that I3C and I2C busses are completely different
>> with little to share between them.
> 
> That wouldn't make sense.
> 
>> To me, the I2C backward compatibility is just a nice feature that was
>> added to help people smoothly transition from mixed I3C busses with
>> both I2C and I3C devices connected to it (I2C devices being here
>> when no (affordable) equivalent exist in the I3C world) to pure I3C
>> busses with only I3C devices connected to it.
> 
> Yeah, and it is still to be seen how good this really works. Devices
> which do clock stretching are out of the question. Probably everything
> which needs an interrupt as well?
> 

I'm surprised they didn't allow for slave clock stretching when
communicating with a legacy i2c device, it will prohibit use of a rather
large class of devices. :(

As for interrupts you are always free to wire up an out-of-band
interrupt like before. :)

>> This being said, I'd be happy if you prove me wrong and propose a
>> solution that allows us to extend the I2C framework to support I3C
>> without to much pain ;-).
> 
> From all I know, I don't see that coming.
>