linux-kernel - Re: [PATCH v2] ACPI / button: make module loadable when booted in non-ACPI mode

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Message-ID: <2286238.nKNuTerCUV@aspire.rjw.lan>
Date:   Mon, 30 Apr 2018 10:04:16 +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 v2] ACPI / button: make module loadable when booted in non-ACPI mode

On Monday, April 23, 2018 11:16:56 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>
> ---
> v2: invert acpi_disabled logic and move comment into __acpi_bus_register_driver
> 
> 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 | 24 +++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
> index e1eee7a60fad..f33242e4fe6c 100644
> --- a/drivers/acpi/button.c
> +++ b/drivers/acpi/button.c
> @@ -635,4 +635,26 @@ 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);
> +static int __acpi_bus_register_driver(struct acpi_driver *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.
> +	 */
> +	if (acpi_disabled)
> +		return 0;
> +	return acpi_bus_register_driver(driver);
> +}
> +
> +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);
> 

Applied (with some minor modifications) and merged into 4.17-rc3, thanks!