Re: [PATCH] hwmon: (corsair-psu) Fix failure to load when built-in to kernel

[Guenter Roeck]

On 12/8/23 08:52, Aleksa Savic wrote:
> On 2023-12-08 16:43:07 GMT+01:00, Guenter Roeck wrote:
> > On 12/8/23 05:57, Wilken Gottwalt wrote:
> > > On Fri, 8 Dec 2023 14:11:44 +0100
> > > Aleksa Savic <savicaleksa83@xxxxxxxxx> wrote:
> > >
> > > > On 2023-12-08 14:07:10 GMT+01:00, Aleksa Savic wrote:
> > > > > When built-in to the kernel, the corsair-psu driver fails to register with
> > > > > the following message:
> > > > >
> > > > > "Driver 'corsair-psu' was unable to register with bus_type 'hid'
> > > > > because the bus was not initialized."
> > > > >
> > > > > Fix this by initializing the driver after the HID bus using
> > > > > late_initcall(), as hwmon is built before HID.
> > > > >
> > > > > Fixes: d115b51e0e56 ("hwmon: add Corsair PSU HID controller driver")
> > > > > Signed-off-by: Aleksa Savic <savicaleksa83@xxxxxxxxx>
> > > > > ---
> > > > >    drivers/hwmon/corsair-psu.c | 15 ++++++++++++++-
> > > > >    1 file changed, 14 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/hwmon/corsair-psu.c b/drivers/hwmon/corsair-psu.c
> > > > > index 904890598c11..48831a528965 100644
> > > > > --- a/drivers/hwmon/corsair-psu.c
> > > > > +++ b/drivers/hwmon/corsair-psu.c
> > > > > @@ -899,7 +899,20 @@ static struct hid_driver corsairpsu_driver = {
> > > > >        .reset_resume    = corsairpsu_resume,
> > > > >    #endif
> > > > >    };
> > > > > -module_hid_driver(corsairpsu_driver);
> > > > > +
> > > > > +static int __init corsairpsu_hid_init(void)
> > > > > +{
> > > > > +    return hid_register_driver(&corsairpsu_driver);
> > > > > +}
> > > > > +
> > > > > +static void __exit corsairpsu_hid_exit(void)
> > > > > +{
> > > > > +    hid_unregister_driver(&corsairpsu_driver);
> > > > > +}
> > > > > +
> > > > > +/* When compiled into the kernel, initialize after the hid bus */
> > > > > +late_initcall(corsairpsu_hid_init);
> > > > > +module_exit(corsairpsu_hid_exit);
> > > > >      MODULE_LICENSE("GPL");
> > > > >    MODULE_AUTHOR("Wilken Gottwalt <wilken.gottwalt@xxxxxxxxxx>");
> > > >
> > > >
> > > > Woops! Just saw that the same fix was sent yesterday. Please disregard, sorry!
> > > >
> > > > Aleksa
> > >
> > > It is fine. I just start to wonder if there was a change in the subsystem. I
> > > used the driver as built-in in the past for several months and never had that
> > > issue. And now it is a real flood of reports.
> >
> > Maybe there was a change in the build order, or some subtle change
> > in driver registration code. Question though is _when_ this changed.
> > It would be great if someone could bisect it. For example, bus registration
> > code has been changed significantly in v6.3. I am copying linux-input
> > and the hid maintainers for feedback.
>
> The late_initcall() was also needed in 2020. when corsair-cpro was added in
> 40c3a4454225 ("hwmon: add Corsair Commander Pro driver").
>
> There was also discussion on the list about it:
>
> https://lore.kernel.org/all/3864498.z6qT3ff8q6@marius/
>
> nzxt-smart2 (from the tail of 2021.) also has a comment about the message.
>
> (Just providing references.)

Ah yes, thanks for the reminder. We actually had a similar problem with
watchdog drivers and worked around it by deferring watchdog driver registration
until the watchdog core is initialized. That is of course just a kludge.
No idea if a clean(er) solution is even possible.

Guenter