linux-kernel - Dell SMBIOS initializing before backends are ready

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Date:   Thu, 8 Feb 2018 18:23:23 +0000
From:   <Mario.Limonciello@...l.com>
To:     <pali.rohar@...il.com>
CC:     <platform-driver-x86@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dvhart@...radead.org>,
        <andy.shevchenko@...il.com>
Subject: Dell SMBIOS initializing before backends are ready

After Paul's recent message regarding the odd wifi issue he had a 
comment I wanted to investigate:

dell_smbios: "No dell-smbios drivers are loaded"

Coming up early in boot.  This is a side effect of dell-smbios having two
backend drivers that can be compiled as modules but no tie to force
them to initialize before calls to dell_smbios_call.

So I believe what is happening is dell_micmute_led_set is called from
the HDA driver and calls dell_smbios_call early too.

I haven't tried it on a platform with mic mute, but I suspect it might cause
the mic mute LED status to be wrong initially (but corrected later when 
toggled).

Ideas that came to mind:

1) In dell_smbios_call if no backends loaded, explicitly do a symbol_request
for both backends and run initialization at that time.

If that works, that would also resolve if someone manually unloaded both
backends but a kernel module still tried to perform a request.

2) Add a notifier chain for when the driver is ready (a backend is loaded)
to all consumers of dell_smbios_call.  Don't let other modules call
dell_smbios_call until notified.
Don't let the HDA driver call dell_micmute_led_set either.

3) try_module_get during dell-smbios initialization for both the backends

What's the correct way to address this?