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Date:   Mon, 25 Oct 2021 18:12:39 +0300
From:   Mika Westerberg <mika.westerberg@linux.intel.com>
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Mario Limonciello <mario.limonciello@outlook.com>,
        Andreas Noever <andreas.noever@gmail.com>,
        Michael Jamet <michael.jamet@intel.com>,
        Yehezkel Bernat <YehezkelShB@gmail.com>,
        linux-usb <linux-usb@vger.kernel.org>
Subject: Re: Disabling intel-wmi-thunderbolt on devices without Thunderbolt /
 detecting if a device has Thunderbolt
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On Mon, Oct 25, 2021 at 04:54:41PM +0200, Hans de Goede wrote:
> > Yes that's exactly what is supposed to happen that this attribute is made.
> > What exactly happens when you write into it?
> 
> The _SB.CGWR ACPI method gets called, with arguments coming from ACPI
> settings stored in memory. Depending on those settings this function
> either directly pokes some MMIO or tries to talk to an I2C GPIO
> expander which is not present on the Surface Go, causing it to
> MMIO poke an I2C controller which it should not touch.
> 
> In either case the AML code ends up poking stuff it should not touch
> and the entire force_power sysfs attribute should simply not be
> there on devices without thunderbolt.

That's right - it should not be there in the first place if there is no
Thunderbolt controller on that thing.

I guess most of the systems that have this actually do support
Thunderbolt so maybe we can work this around by quirking all the Surface
models in that driver?