linux-kernel - Re: [PATCH v1 0/2] i2c: Stop i2c modules being unloaded while in use.

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Message-ID: <91828685-c7ba-b5b2-f128-240fdf9ebb44@mentor.com>
Date:   Tue, 13 Sep 2016 17:55:50 +0100
From:   "Baxter, Jim" <jim_baxter@...tor.com>
To:     Peter Rosin <peda@...ntia.se>, <linux-i2c@...r.kernel.org>
CC:     Peter Korsgaard <peter.korsgaard@...co.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        <linux-kernel@...r.kernel.org>,
        "Frkuska, Joshua" <Joshua_Frkuska@...tor.com>,
        jiwang <Jiada_Wang@...tor.com>
Subject: Re: [PATCH v1 0/2] i2c: Stop i2c modules being unloaded while in use.

Hi Peter,

> nitpick: Patch subjects for the second patch is wrong.
>
> "reparented" is a bit dual when dealing with i2c adapter trees.
> i2c_mux_add_owned_adapter is perhaps clearer?

Agreed, I will update that.

>
>
> Aside from that, I'm not using modules much and need some enlightenment
> as to why the i2c_del_mux_adapter() call in i2c_mux_gpio_remove() is not
> sufficient and what exactly the problem is? Why would someone/something
> unload the i2c-mux module prematurely?

It is not a normal operation to remove the i2c gpio mux, however systemd
could unload modules out of order if users are restarting services
incorrectly and cause unintended side-effects. This change would stop an
i2c-mux that maybe controlling a voltage regulator from being unloaded
and disabling power to parts of the system unexpectedly.

>
>
> Would it be an alternative to make i2c-mux a proper kernel object of
> some kind? I mean, why do not all other mux users also need to modify
> the owner? Why is i2c-mux-gpio special?
>

i2c-mux-gpio is not special, the code inserted by
[PATCH v1 1/2] i2c-mux: add i2c_mux_add_reparented_adapter api could be
used by other muxes if required.

Best regards
Jim