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

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Date:   Fri, 30 Aug 2019 11:35:08 -0700
From:   Ray Jui <ray.jui@...adcom.com>
To:     Wolfram Sang <wsa@...-dreams.de>,
        Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
Cc:     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 8/30/19 5:56 AM, Wolfram Sang wrote:
> Hi everyone,
> 
>> +/*
>> + * If 'process_call' is true, then this is a multi-msg transfer that requires
>> + * a repeated start between the messages.
>> + * More specifically, it must be a write (reg) followed by a read (data).
>> + * The i2c quirks are set to enforce this rule.
>> + */
> 
> 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)?

1) Does
>> +	/* Process the read message if this is process call */
> 
> Also, the term "process call" here seriously sounds like SMBus.
> 
>> +		addr = msg->addr << 1 | 1;
> 
> addr = i2c_8bit_addr_from_msg(msg);
> 
>> +		u32 protocol;
> 
> Hmm, another SMBus terminology.
> 
> 
>> +	if (num > 2) {
>> +		dev_err(iproc_i2c->device,
>> +			"Only support up to 2 messages. Current msg count %d\n",
>> +			num);
>> +		return -EOPNOTSUPP;
>> +	}
> 
> With your quirks flags set, the core checks it for you.
> 
> Kind regards,
> 
>     Wolfram
>