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

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Message-ID: <540c4e2d-0dd5-5260-30b2-e1589b279d71@broadcom.com>
Date:   Tue, 3 Sep 2019 16:11:16 -0700
From:   Ray Jui <ray.jui@...adcom.com>
To:     Wolfram Sang <wsa@...-dreams.de>
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



On 8/31/19 2:49 AM, Wolfram Sang wrote:
> Hi Ray,
> 
>>> With all the limitations in place, I wonder if it might be easier to
>>> implement an smbus_xfer callback instead? What is left that makes this
>>> controller more than SMBus and real I2C?
>>>
>>
>> Right. But what is the implication of using smbus_xfer instead of
>> master_xfer in our driver?
>>
>> Does it mean it will break existing functions of the i2c app that our
>> customers developed based on i2cdev (e.g., I2C_RDWR)?
> 
> If the customers uses I2C_RDWR (and it cannot be mapped to i2c_smbus_*
> calls) then this is an indication that there is some I2C functionality
> left which the HW can provide. I'd be interested which one, though.
> 
>>
>> 1) Does
> 
> Maybe you wanted to describe it here and it got accidently cut off? >

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.

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?

Thanks,

Ray

> Regards,
> 
>     Wolfram
>