[PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device API

[Geert Uytterhoeven]

Hi Laurent,

On Wed, May 31, 2023 at 10:59 AM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
> On Mon, May 29, 2023 at 09:00:43AM +0000, Biju Das wrote:
> > > Subject: Re: [PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device API
> > > And why do you need this ?
> >
> > As per Krzysztof [2],
> >
> > The DT schema allows multiple addresses for children. But we lack
> > implementation of parent child relationship, As parent owns the resources.
> > Child device needs to parse parent node to get some resource
> > like clocks.
> >
> > [2] https://lore.kernel.org/linux-renesas-soc/TYCPR01MB5933BFFD4EB556F5FB4EA82186729@TYCPR01MB5933.jpnprd01.prod.outlook.com/
>
> The I2C ancillary clients are not meant to be handled by separate
> drivers. You're supposed to have one device node in DT, which causes the
> I2C core to instantiate a main i2c_client, and bind it to one driver.
> That driver then uses i2c_new_ancillary_device() to create other
> i2c_client instances for the secondary I2C addresses. Those i2c_client
> instances are not bound to a separate driver, so there should be no code
> that needs to look at the parent for resources.

In Biju's particular use case, the i2c device responds to two addresses,
which is the standard i2c ancillary use case.  However, what's special
is that the second instance is a derivative of an existing i2c device
with an existing Linux driver.  Hence the desire to make the existing
driver match against the second instance, which requires these changes
to i2c_new_ancillary_device().

As some resources are shared (knowledge about the clocks), splitting
this in two distinct devices in DT (which is what Biju's initial patch
series did) would need phandles to link both nodes together.

Do you have a better idea how to represent this?

Wolfram: time to chime in ;-)

Thanks!


Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds