linux-kernel - Re: [PATCH RFC] modpost: Support I2C Aliases from OF tables

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Date:   Tue, 6 Aug 2019 09:22:39 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH RFC] modpost: Support I2C Aliases from OF tables

Hi Javier,

On Tue, Aug 6, 2019 at 12:25 AM Javier Martinez Canillas
<javierm@...hat.com> wrote:
> On 7/31/19 9:44 PM, Wolfram Sang wrote:
> > Hi Javier,
> >> The other option is to remove i2c_of_match_device() and don't make OF match
> >> to fallback to i2c_of_match_device_sysfs(). This is what happens in the ACPI
> >> case, since i2c_device_match() just calls acpi_driver_match_device() directly
> >> and doesn't have a wrapper function that fallbacks to sysfs matching.
> >>
> >> In this case an I2C device ID table would be required if the devices have to
> >> be instantiated through sysfs. That way the I2C table would be used both for
> >> auto-loading and also to match the device when it doesn't have an of_node.
> >
> > That would probably mean that only a minority of drivers will not add an I2C
> > device ID table because it is easy to add an you get the sysfs feature?
> >
>
> I believe so yes.

> As Masahiro-san mentioned, this approach will still require to add a new macro
> MODULE_DEVICE_TABLE(i2c_of, bar_of_match) so the OF device table is used twice.
>
> One to expose the "of:N*T*Cfoo,bar" and another one to expose it as "i2c:bar".
>
> I expect that many developers would miss adding this macro for new drivers that
> are DT-only and so sysfs instantiation would not work there. So whatever is the
> approach taken we should clearly document all this so drivers authors are aware.

You could add a new I2C_MODULE_DEVICE_TABLE() that adds both, right?
Makes it a little bit easier to check/enforce this.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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