Re: [PATCH 2/3] iio: light: stk3310: add per-chip match data

[Jorijn van der Graaf <jorijnvdgraaf@catcrafts.net>]

On Mon, Aug 10, 2026 at 09:34:42PM +0300, Andy Shevchenko wrote:
> > +	chip_info = i2c_get_match_data(client);
> > +	if (!chip_info) {
> > +		/*
> > +		 * Clients instantiated through the sysfs new_device
> > +		 * interface under the lowercase compatible-derived name
> > +		 * have no firmware node and do not match the uppercase
> > +		 * id table entries.
> > +		 */
> > +		chip_info = &stk3310_chip_info;
>
> This is an interesting comment and approach.
>
> > +	}
>
> - Where does this lowercase come from? Is it Linux forced conversion?

No conversion - the client name is whatever is echoed into the sysfs
new_device file, and the lowercase spelling is the one that binds via
the OF table: for a client with no firmware node,
i2c_of_match_device() falls through to i2c_of_match_device_sysfs(),
which matches the client name against each compatible and its part
after the vendor prefix, so "stk3310" binds through
"sensortek,stk3310" - the same lowercase name a DT client gets from
of_alias_from_compatible(). The id table lookup stays case-sensitive,
which is why i2c_get_match_data() comes back NULL for such a client:
device_get_match_data() needs the firmware node it does not have, and
i2c_match_id() only knows the historic uppercase names.

> - What's wrong with simply failing the probe?

It would break a path that works before this patch: probe consumed no
match data, so "echo stk3310 0x48 > new_device" bound and probed fine
(we used exactly that during bring-up, before the DT node existed).
Failing it would be a userspace-visible regression in a patch that
claims no functional change.

> As far as I understand the problem is preexisted. Or was there any default
> taken? How do we know that the chosen default is a good one?

The path preexists; only this patch makes probe care about match
data. Before it the driver had no per-chip data at all - every client
got the same two channels and the hardcoded "stk3310" name however it
matched. The fallback selects stk3310_chip_info, which is exactly
that, so a client that probed before this patch behaves identically
after it. What the default cannot give is the new part's extra
channels: an STK36C61 instantiated under the lowercase name gets the
reduced legacy profile, and the id table spelling "STK36C61" selects
the full one.

Thanks,
Jorijn