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

[Eddie James]

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@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.
> 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