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Date:   Sun, 4 Feb 2018 19:29:54 +0300
From:   Alexander Sergeyev <sergeev917@gmail.com>
To:     Pali =?iso-8859-1?Q?Roh=E1r?= <pali.rohar@gmail.com>
Cc:     Mario.Limonciello@dell.com, dvhart@infradead.org,
        andy@infradead.org, linux-kernel@vger.kernel.org,
        mjg59@srcf.ucam.org, platform-driver-x86@vger.kernel.org
Subject: Re: PROBLEM: NULL pointer dereference in dell_set_arguments() in 4.15
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>To make dell_micmute_led_set() work properly we need to ensure that either WMI 
>or SMM driver is already loaded and initialized.

From the looks of the call trace dell_micmute_led_set() is called from device 
phase of initialization. Which means that there is a use of dell-laptop 
interface while the module is not initialized (since late_initcall). 
Previously, this led to crashes.

But dell_micmute_led_set() does not touch the module state now, so nothing is 
technically broken; dell-smbios and dell-smbios-smm use subsys_initcall, so 
they are ready. But WMI driver is in the same phase with intel hda, so there 
might be something there.