linux-kernel - Re: [PATCH v5 0/6] drivers/i2c: Add FSI-attached I2C master algorithm

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Message-Id: <7802dc48-6850-b7e3-5dbf-ee333cdf0c83@linux.vnet.ibm.com>
Date:   Tue, 15 Aug 2017 12:53:52 -0500
From:   Eddie James <eajames@...ux.vnet.ibm.com>
To:     Peter Rosin <peda@...ntia.se>,
        Christopher Bostic <cbostic@...ux.vnet.ibm.com>,
        Joel Stanley <joel@....id.au>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-i2c@...r.kernel.org, devicetree <devicetree@...r.kernel.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Rob Herring <robh+dt@...nel.org>, Jeremy Kerr <jk@...abs.org>,
        Andrew Jeffery <andrew@...id.au>,
        "Edward A. James" <eajames@...ibm.com>
Subject: Re: [PATCH v5 0/6] drivers/i2c: Add FSI-attached I2C master algorithm



On 08/15/2017 12:35 PM, Peter Rosin wrote:
> On 2017-08-15 18:28, Christopher Bostic wrote:
>> On 8/15/17 3:10 AM, Joel Stanley wrote:
>>> On Tue, Aug 15, 2017 at 4:06 PM, Peter Rosin <peda@...ntia.se> wrote:
>>>> On 2017-07-26 19:13, Eddie James wrote:
>>>>> From: "Edward A. James" <eajames@...ibm.com>
>>>>>
>>>>> This series adds an algorithm for an I2C master physically located on an FSI
>>>>> slave device. The I2C master has multiple ports, each of which may be connected
>>>>> to an I2C slave. Access to the I2C master registers is achieved over FSI bus.
>>>>>
>>>>> Due to the multi-port nature of the I2C master, the driver instantiates a new
>>>>> I2C adapter for each port connected to a slave. The connected ports should be
>>>>> defined in the device tree under the I2C master device.
>>>> Hmmm, AFAIU fsi is a bus, and on this bus you have some "client" device that
>>>> happens to be an i2c master, and this is a driver for that "client". Is it
>>>> totally inconceivable to have some other client device in the future that is
>>>> implementing an i2c master differently, but still using the fsi bus?
>>>>
>>>> With that in mind, is it wise to pick the driver name from the bus that the
>>>> device is connected to, and nothing else without further qualification?
>>>>
>>>> I don't see any "i2c-usb" driver, but I think there are a couple of i2c master
>>>> drivers that communicate via usb.
>>> You make a fair point. When I did a prototype of this driver I called
>>> it i2c-cfam, as it is part of the CFAM hardware unit inside of the
>>> Power8/Power9 processors.
>>>
>>> The documentation does call it FSI_I2CM, so that's an argument for the
>>> current name.
>>>
>>> I'm not sure how accurate that name is. Chris, Eddie, do you have any
>>> other suggestions?
>> The I2C engine up to now has been always accessed via the FSI bus so
>> historically I assume that's why its labelled as FSI_I2CM in the p8/p9
>> specs.  There isn't any reason this I2C device couldn't be implemented
>> in some other topology independent of FSI / CFAMs.  In other words there
>> are no FSI details internal to this I2C engine, an argument for removing
>> the 'FSI' tag.
> Note that I wasn't primarily concerned with this i2c engine growing some other
> non-fsi interface (like many devices have both i2c and spi interface versions).
> I was more concerned with some future and totally different i2c engine that
> naturally sports a totally different register map but still uses the fsi bus.
>
> But you have a point. If this i2c engine evolves and ends up supporting some
> other interface, then that too would be cause to regret the i2c-fsi name.

i2c-cfam would work, though it would also be possible for another type 
of i2c engine to exist on a CFAM... it has been done in the past.

Historically, this driver was called "iic-boe" for "Boeblingen". I'm not 
suggesting it's a good name for this driver, but it is unique...

Edduie

>
> Cheers,
> peda
>