Re: [PATCH v9 3/3] HID: cp2112: Fwnode Support

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

+Cc: Niyas, who is working a lot on filling the gaps in ACPI in comparison
     to DT in the Linux kernel. Perhaps he has some ideas or even better
     solutions.

On Mon, May 01, 2023 at 06:35:44PM -0500, Daniel Kaehn wrote:
> On Mon, Mar 20, 2023 at 9:10 AM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Mon, Mar 20, 2023 at 08:40:07AM -0500, Daniel Kaehn wrote:
> > > On Mon, Mar 20, 2023 at 8:00 AM Andy Shevchenko
> > > <andriy.shevchenko@linux.intel.com> wrote:
> > > > On Mon, Mar 20, 2023 at 02:58:07PM +0200, Andy Shevchenko wrote:
> > > > > On Sun, Mar 19, 2023 at 03:48:02PM -0500, Danny Kaehn wrote:

...

> > > > > > +   device_for_each_child_node(&hdev->dev, child) {
> > > > > > +           name = fwnode_get_name(child);
> > > > > > +           ret = acpi_get_local_address(ACPI_HANDLE_FWNODE(child), &addr);
> > > > > > +
> > > > > > +           if ((name && strcmp("i2c", name) == 0) || (!ret && addr == 0))
> > > > > > +                   device_set_node(&dev->adap.dev, child);
> > > > > > +           else if ((name && strcmp("gpio", name)) == 0 ||
> > > > > > +                                   (!ret && addr == 1))
> > > > > > +                   dev->gc.fwnode = child;
> > > > > > +   }
> > > > >
> > > > > Please, make addresses defined explicitly. You may also do it with node naming
> > > > > schema:
> > > > >
> > > > > #define CP2112_I2C_ADR                0
> > > > > #define CP2112_GPIO_ADR               1
> > > > >
> > > > > static const char * const cp2112_cell_names[] = {
> > > > >       [CP2112_I2C_ADR]        = "i2c",
> > > > >       [CP2112_GPIO_ADR]       = "gpio",
> > > > > };
> > > > >
> > > > >       device_for_each_child_node(&hdev->dev, child) {
> > > > >               name = fwnode_get_name(child);
> > > > >               if (name) {
> > > > >                       ret = match_string(cp2112_cell_names, ARRAY_SIZE(cp2112_cell_names), name);
> > > > >                       if (ret >= 0)
> > > > >                               addr = ret;
> > > > >               } else
> > > > >                       ret = acpi_get_local_address(ACPI_HANDLE_FWNODE(child), &addr);
> > > > >               if (ret < 0)
> > > > >                       ...error handling if needed...
> > > > >
> > > > >               switch (addr) {
> > > > >               case CP2112_I2C_ADR:
> > > > >                       device_set_node(&dev->adap.dev, child);
> > > > >                       break;
> > > > >               case CP2112_GPIO_ADR:
> > > > >                       dev->gc.fwnode = child;
> > > > >                       break;
> > > > >               default:
> > > > >                       ...error handling...
> > > > >               }
> > > > >       }
> > > >
> > > > Btw, don't you use "reg" property for the child nodes? It would be better from
> > > > de facto used patterns (we have a couple of mode drivers that have a common
> > > > code to read "reg" or _ADR() and that code can be split into a helper and used
> > > > here).
> > >
> > > Named nodes _seem_ to be preferred in DT for when there isn't a logical /
> > > natural numbering to the child nodes. A.e. for USB, reg is used to specify
> > > which port, for I2C, which address on the bus, but for two parallel and
> > > independent functions on the same device, it seems named nodes would make
> > > more sense in DT. Many examples exist in mainline where named nodes are used
> > > in DT in this way.
> >
> > Okay, I'm not an expert in the DT preferable schemas, so I believe DT people
> > should answer on this.
> 
> Hello,
> 
> Thanks for all the time spent reviewing this thus far. Following up to
> see what my next steps might be.
> 
> It sounds like we might want some DT folks to weigh in on the strategy
> used for identifying the child I2C and GPIO nodes for the CP2112
> device before moving further toward applying this.
> 
> Since the DT list is on this thread (as well as Rob+Krzystof), and
> this has sat for a little while, I'm assuming that the ball is in my
> court to seek out an answer/opinion here. (I know folks get a lot of
> email, so apologies if the correct move would have been to wait a bit
> longer before following up! Not intending to be rude.)
> 
> Would it be appropriate / expected that I send a separate email thread
> to the DT mailing list on their opinion here? Or would that create
> more confusion/complexity in adding yet another thread? I did create a
> separate email thread for the initial DT vs. ACPI conversation we had
> about accessing children by name or index in a unified way due to the
> differences in upper/lower case and use-cases, but that
> (understandably) didn't seem to gain any traction.
> 
> Thanks for any insights!
> 
> Thanks,
> Danny Kaehn
> 
> > > One example is network cards which provide an mdio bus
> > > bind through the child "mdio". One example of a specifically a
> > > child i2c controller being bound to "i2c" can be found in
> > > pine64,pinephone-keyboard.yaml.
> > > But it's certainly possible this isn't the desired direction moving forward
> > > in DT -- my opinion should definitely be taken with a grain of salt. Maybe
> > > this is something I should follow up on with DT folks on that DT vs. ACPI
> > > thread made earlier.
> > >
> > > One thing I did notice when looking at the mfd subsystem is that most DT
> > > drivers actually match on the compatible string of the child nodes, a.e.
> > > "silabs,cp2112", "silabs,cp2112-gpio".  "silabs,cp2112-i2c". We could
> > > implement that here, but I think that would make more sense if we were to
> > > actually split the cp2112 into mfd & platform drivers, and additionally split
> > > the DT binding by function.
> >
> > IIRC (but might be very well mistaken) the compatible strings for children
> > are discouraged.

-- 
With Best Regards,
Andy Shevchenko