Re: [PATCH v7 1/7] i2c: add I2C Address Translator (ATR) support

[Tomi Valkeinen]

On 19/01/2023 13:35, Luca Ceresoli wrote:
> Hi Tomi, Andy,
>
> On Thu, 19 Jan 2023 12:09:57 +0200
> Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote:
>
> > On 19/01/2023 10:21, Luca Ceresoli wrote:
> >
> > <snip>
> >
> > > > > > > +void i2c_atr_set_driver_data(struct i2c_atr *atr, void *data)
> > > > > > > +{
> > > > > > > +	atr->priv = data;
> > > > > > > +}
> > > > > > > +EXPORT_SYMBOL_NS_GPL(i2c_atr_set_driver_data, I2C_ATR);
> > > > > > > +
> > > > > > > +void *i2c_atr_get_driver_data(struct i2c_atr *atr)
> > > > > > > +{
> > > > > > > +	return atr->priv;
> > > > > > > +}
> > > > > > > +EXPORT_SYMBOL_NS_GPL(i2c_atr_get_driver_data, I2C_ATR);
> > > > > >
> > > > > > Just to be sure: Is it really _driver_ data and not _device instance_ data?
> > > > >
> > > > > It is device instance data indeed. I don't remember why this got
> > > > > changed, but in v3 it was i2c_atr_set_clientdata().
> > > >
> > > > It's me who was and is against calling it clientdata due to possible
> > > > confusion with i2c_set/get_clientdata() that is about *driver data*.
> > > > I missed that time the fact that this is about device instance data.
> > > > I dunno which name would be better in this case, i2c_atr_set/get_client_priv() ?
> > >
> > > Not sure I'm following you here. The i2c_atr_set_clientdata() name was
> > > given for similarity with i2c_set_clientdata(). The latter wraps
> > > dev_set_drvdata(), which sets `struct device`->driver_data. There is
> > > one driver_data per each `struct device` instance, not per each driver.
> > > The same goes for i2c_atr_set_driver_data(): there is one priv pointer
> > > per each `struct i2c_atr` instance.
> >
> > I'm a bit confused. What is "driver data" and what is "device instance
> > data"?
> >
> > This deals with the driver's private data, where the "driver" is the
> > owner/creator of the i2c-atr. The i2c-atr itself doesn't have a device
> > (it's kind of part of the owner's device), and there's no driver in
> > i2c-atr.c
> >
> > I don't like "client" here, as it reminds me of i2c_client (especially
> > as we're in i2c context).
> >
> > What about i2c_atr_set_user_data()? Or "owner_data"?
>
> Ah, only now I got the point Andy made initially about "client" not
> being an appropriate word.
>
> In i2c we have:
>
>    i2c_set_clientdata(struct i2c_client *client, void *data)
>            ^^^^^^~~~~            ^^^^^^                ~~~~
>
> so "client" clearly makes sense there, now here.

Isn't that also used by the i2c_client? A driver which handles an i2c 
device is the "i2c client", in a sense?

> The same logic applied here would lead to:
>
>    i2c_atr_set_atrdata(struct i2c_atr *atr, void *data)
>                ^^^~~~~            ^^^             ~~~~
>
> which makes sense but it is a ugly IMO.

Here, I think, there's a bit of a difference to the i2c_client case, as 
we have a separate component for the i2c-atr. Although I guess one can 
argue that the top level driver is the ATR driver, as it handles the HW, 
and i2c-atr.c is just a set of helpers, so... I don't know =).

> So I think i2c_atr_get_driver_data() in this v7 makes sense, it's to
> set the data that the ATR driver instance needs.
>
> This is coherent with logic in spi/spi.h:
>
>    spi_set_drvdata(struct spi_device *spi, void *data)
>
> except for the abbreviation ("_drvdata" vs "_driver_data").
>
> Andy, Tomi, would i2c_atr_set_drvdata() be OK for you, just like SPI
> does?

Well, I'm good with the current i2c_atr_set_driver_data(). If all agrees 
that it's "driver data", I'd rather keep it like that. I find this 
"drvdata" style very odd. Why no underscore between drv and data? Why 
abbreviate drv, it doesn't really help anything here?

That said, I'm also fine with i2c_atr_set_drvdata if that's the popular 
opinion (between the three of us, so far ;).

 Tomi