linux-kernel - Re: [PATCH] ACPI / button: make module loadable when booted in non-ACPI mode

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Date:   Mon, 23 Apr 2018 11:11:36 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, arnd@...db.de, broonie@...nel.org,
        lorenzo.pieralisi@....com, bill.fletcher@...aro.org,
        linux-arm-kernel@...ts.infradead.org, graeme.gregory@...aro.org
Subject: Re: [PATCH] ACPI / button: make module loadable when booted in non-ACPI mode

On Monday, April 23, 2018 10:28:34 AM CEST Ard Biesheuvel wrote:
> Modules such as nouveau.ko and i915.ko have a link time dependency on
> acpi_lid_open(), and due to its use of acpi_bus_register_driver(),
> the button.ko module that provides it is only loadable when booted in
> ACPI mode. However, the ACPI button driver can be built into the core
> kernel as well, in which case the dependency can always be satisfied,
> and the dependent modules can be loaded regardless of whether the
> system was booted in ACPI mode or not.
> 
> So let's fix this asymmetry by making the ACPI button driver loadable
> as a module even if not booted in ACPI mode, so it can provide the
> acpi_lid_open() symbol in the same way as when built into the kernel.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
> Could we perhaps get this into -stable as well? It is not a classic
> regression, but it completely breaks, e.g., Fedora when booting in
> DT mode on an ARM system.
> 
>  drivers/acpi/button.c | 23 +++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
> index e1eee7a60fad..0506ca56c615 100644
> --- a/drivers/acpi/button.c
> +++ b/drivers/acpi/button.c
> @@ -635,4 +635,25 @@ module_param_call(lid_init_state,
>  		  NULL, 0644);
>  MODULE_PARM_DESC(lid_init_state, "Behavior for reporting LID initial state");
>  
> -module_acpi_driver(acpi_button_driver);
> +/*
> + * Modules such as nouveau.ko and i915.ko have a link time dependency on
> + * acpi_lid_open(), and would therefore not be loadable on ACPI capable kernels
> + * booted in non-ACPI mode if we use the ordinary acpi_bus_[un]register_driver
> + * routines here (which only work when booted in ACPI mode) and build this
> + * driver as a module. So provide our own versions instead.
> + */
> +static int __acpi_bus_register_driver(struct acpi_driver *driver)
> +{
> +	if (!acpi_disabled)
> +		return acpi_bus_register_driver(driver);
> +	return 0;
> +}

I would write this as:

    if (acpi_disabled)
            return 0;

    return acpi_bus_register_driver(driver);

and the comment can go above the (acpi_disabled) check then (bacause that's
what makes the difference when ACPI is disabled).

> +
> +static void __acpi_bus_unregister_driver(struct acpi_driver *driver)
> +{
> +	if (!acpi_disabled)
> +		acpi_bus_unregister_driver(driver);
> +}
> +
> +module_driver(acpi_button_driver, __acpi_bus_register_driver,
> +	      __acpi_bus_unregister_driver);
>