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

[Luca Ceresoli]

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.

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.

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?

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com