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

[Christopher Bostic]

On 8/15/17 3:10 AM, Joel Stanley wrote:
> On Tue, Aug 15, 2017 at 4:06 PM, Peter Rosin <peda@xxxxxxxxxx> wrote:
> > On 2017-07-26 19:13, Eddie James wrote:
> > > From: "Edward A. James" <eajames@xxxxxxxxxx>
> > >
> > > 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.

Thanks,
Chris

> Cheers,
>
> Joel