linux-kernel - Re: [PATCH] hwmon: (corsair-psu) Fix probe when built-in

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Message-ID: <20231208074802.56bb2d78@posteo.net>
Date:   Fri,  8 Dec 2023 06:48:02 +0000
From:   Wilken Gottwalt <wilken.gottwalt@...teo.net>
To:     Armin Wolf <W_Armin@....de>
Cc:     jdelvare@...e.com, linux@...ck-us.net, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (corsair-psu) Fix probe when built-in

On Thu,  7 Dec 2023 22:07:23 +0100
Armin Wolf <W_Armin@....de> wrote:

> It seems that when the driver is built-in, the HID bus is
> initialized after the driver is loaded, which whould cause
> module_hid_driver() to fail.
> Fix this by registering the driver after the HID bus using
> late_initcall() in accordance with other hwmon HID drivers.
> 
> Compile-tested only.

So you did not test this? Well, I did.

[    2.225831] Driver 'corsair-psu' was unable to register with bus_type 'hid' because the bus was not initialized.
[    2.225835] amd_pstate: driver load is disabled, boot with specific mode to enable this
[    2.226363] ledtrig-cpu: registered to indicate activity on CPUs
[    2.226679] hid: raw HID events driver (C) Jiri Kosina

You are right, it is a timing issue and this can actually happen. I'm fine with
the fix.

Though, this could even be a bigger issue. There are currently 104 HID drivers
using the module_hid_driver macro. Maybe it would be a better idea to change the
module_hid_driver macro to use the lateinit calls instead of the plain init/exit
calls.

greetings,
Will

> Signed-off-by: Armin Wolf <W_Armin@....de>
> ---
>  drivers/hwmon/corsair-psu.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/corsair-psu.c b/drivers/hwmon/corsair-psu.c
> index 904890598c11..2c7c92272fe3 100644
> --- a/drivers/hwmon/corsair-psu.c
> +++ b/drivers/hwmon/corsair-psu.c
> @@ -899,7 +899,23 @@ static struct hid_driver corsairpsu_driver = {
>  	.reset_resume	= corsairpsu_resume,
>  #endif
>  };
> -module_hid_driver(corsairpsu_driver);
> +
> +static int __init corsair_init(void)
> +{
> +	return hid_register_driver(&corsairpsu_driver);
> +}
> +
> +static void __exit corsair_exit(void)
> +{
> +	hid_unregister_driver(&corsairpsu_driver);
> +}
> +
> +/*
> + * With module_init() the driver would load before the HID bus when
> + * built-in, so use late_initcall() instead.
> + */
> +late_initcall(corsair_init);
> +module_exit(corsair_exit);
> 
>  MODULE_LICENSE("GPL");
>  MODULE_AUTHOR("Wilken Gottwalt <wilken.gottwalt@...teo.net>");
> --
> 2.39.2
>