linux-kernel - Re: [PATCH v1 1/1] i2c: iproc: Add i2c repeated start capability

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Message-ID: <20190904213745.GG23608@ninjato>
Date:   Wed, 4 Sep 2019 23:37:45 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Ray Jui <ray.jui@...adcom.com>
Cc:     Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Lori Hikichi <lori.hikichi@...adcom.com>,
        Icarus Chau <icarus.chau@...adcom.com>,
        Shivaraj Shetty <sshetty1@...adcom.com>
Subject: Re: [PATCH v1 1/1] i2c: iproc: Add i2c repeated start capability


> I think you are right that the controller does not seem to support
> additional I2C features in addition to SMBUS.
> 
> However, my concern of switching to the smbus_xfer API is:
> 
> 1) Some customers might have used I2C_RDWR based API from i2cdev. Changing
> from master_xfer to smbus_xfer may break the existing applications that are
> already developed.

Well, given that you add new quirks in the original patch here, you are
kind of breaking it already. Most transfers which are not SMBus-alike
transfers would now be rejected. For SMBus-alike transfers which are
sent via I2C_RDWR (which is ugly), I have to think about it.

> 2) The sound subsystem I2C regmap based implementation seems to be using
> i2c_ based API instead of smbus_ based API. Does this mean this will also
> break most of the audio codec drivers with I2C regmap API based usage?

I don't think so. If you check regmap_get_i2c_bus() then it checks the
adapter functionality and chooses the best transfer option then. I may
be missing something but I would wonder if the sound system does
something special and different.


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