Re: [PATCH v2 2/6] platform/x86: dell-smo8800: Move instantiation of lis3lv02d i2c_client from i2c-i801 to dell-smo8800

Pali Rohár
2024-02-29T20:46:15Z

On Wednesday 28 February 2024 13:50:27 Hans de Goede wrote:
> Hi,
>
> On 2/27/24 23:37, Andy Shevchenko wrote:
> > On Tue, Feb 27, 2024 at 11:50 PM Pali Rohár <pali@kernel.org> wrote:
> >> On Tuesday 27 February 2024 23:19:19 Andy Shevchenko wrote:
> >>> On Tue, Feb 27, 2024 at 11:04 PM Pali Rohár <pali@kernel.org> wrote:
> >
> > ...
> >
> >>> I'm wondering why we need all this. We have notifiers when a device is
> >>> added / removed. We can provide a board_info for the device and attach
> >>> it to the proper adapter, no?
> >>
> >> I do not know how flexible are notifiers. Can notifier call our callback
> >> when new "struct i2c_adapter *adapter" was instanced?
> >
> > You can follow notifications of *an* I2C adapter being added /
> > removed. With that, you can filter which one is that. Based on that
> > you may attach a saved (at __init as you talked about in the reply to
> > Hans) board_info with all necessary information.
> >
> > Something like this (combined)
> > https://elixir.bootlin.com/linux/latest/source/drivers/ptp/ptp_ocp.c#L4515
> > https://elixir.bootlin.com/linux/latest/source/drivers/input/mouse/psmouse-smbus.c#L194
>
> drivers/platform/x86/touchscreen_dmi.c actually already does something
> like this for i2c-clients. The problem is that this brings probe-ordering
> problems with it. If the i801 driver is loaded before the dell-smo8800
> driver then the notifiers will not trigger since the i2c-adapter has
> already been created (1).
>
> So we would still need a "cold-plug" manual scan in smo8800_probe()
> anyways at which point we might as well just return -EPROBE_DEFER
> when the adapter is not there.

And that it example why the current existing solution is better, it does
not have such problems like the proposed.

> As for Pali's suggestion of having the i2c-i801 code call a symbol
> exported by dell-smo8800

I did not suggest that! Please do not make false statements about me.

> that will cause the dell-smo8800 driver
> to load on all x86 devices with an i2c-i801 controller (pretty
> much all of them). Slowing the boot and eating memory.