Re: [PATCH v1 2/3] auxdisplay: ht16k33: Make use of device_get_match_data()

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

On Wed, Feb 22, 2023 at 07:46:25PM +0100, Krzysztof Kozlowski wrote:
> On 22/02/2023 18:20, Andy Shevchenko wrote:
> >>
> >>> Which effectively breaks i.e. user-space instantiation for other display
> >>> types which now do work due to i2c_of_match_device().
> >>> (so my suggestion above is not sufficient).
> >>>
> >>> Are you proposing extending and searching the I2C ID table to work around
> >>> that?
> >>
> >> See (1) above. This is the downside I have noticed after sending this series.
> >> So, the I²C ID table match has to be restored, but the above mentioned issues
> >> with existing table are not gone, hence they need to be addressed in the next
> >> version.
> > 
> > I see now what you mean. So, we have even more issues in this driver:
> > - I²C table is not in sync with all devices supported
> 
> Does anything actually rely on i2c_device_id table? ACPI would match
> either via ACPI or OF tables. All modern ARM systems (e.g. imx6) are
> DT-based. Maybe just drop the I2C ID table?

For I²C it's still possible to enumerate the device via sysfs, which is ABI.

> > - the OF ID table seems has something really badly formed for adafruit
> >   (just a number after a comma)
> 
> Maybe it is a model number? It was documented:
> Documentation/devicetree/bindings/auxdisplay/holtek,ht16k33.yaml

Yes, it's not a problem for ACPI/DT platforms, the problem is for the above
way of enumeration, so if we have more than 1 manufacturer that uses plain
numbers for the model, I²C framework may not distinguish which driver to use.

I.o.w. the part after comma in the compatible strings of the I²C devices must
be unique globally to make that enumeration disambiguous.

> > The latter shows how broken it is. The I²C ID table mechanism is used as
> > a backward compatibility to the OF. Unfortunately, user space may not provide
> > the data except in form of DT overlays, so for the legacy enumeration we
> > have only device name, which is a set of 4 digits for adafruit case.
> > 
> > Now imagine if by some reason we will get adafruit2 (you name it) with
> > the same schema. How I²C framework can understand that you meant adafruit
> > and not adafruit2? Or did I miss something?

-- 
With Best Regards,
Andy Shevchenko