linux-kernel - Re: Fwd: [PATCH] Add driver to force WMI Thunderbolt controller power status

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Date:   Wed, 6 Sep 2017 19:40:59 +0000
From:   "Bernat, Yehezkel" <yehezkel.bernat@...el.com>
To:     "mario.limonciello@...l.com" <mario.limonciello@...l.com>
CC:     "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.ke" <platform-driver-x86@...r.ke>,
        "dvhart@...radead.org" <dvhart@...radead.org>,
        "hughsient@...il.com" <hughsient@...il.com>
Subject: Re: Fwd: [PATCH] Add driver to force WMI Thunderbolt controller power
 status


> Current implementations of Intel Thunderbolt controllers will go
> into a low power mode when not in use.
> 
> Many machines containing these controllers also have a GPIO wired up
> that can force the controller awake.  This is offered via a ACPI-WMI
> interface intended to be manipulated by a userspace utility.


> This mechanism is provided by Intel to OEMs to include in BIOS.
> It uses an industry wide GUID that is populated in a separate _WDG
> entry with no binary MOF.
> 
> This interface allow software such as fwupd to wake up thunderbolt
> controllers to query the firmware version or flash new firmware.

As this is a Thunderbolt specific function, maybe it's better to be
exposed from the Thunderbolt driver?


> +
> +static DEVICE_ATTR_WO(force_power);
> +

I'm not sure what is the convention for permissions for this type of
attributes but I feel like this worth being root-only writable, as it
can be used to power-off the controller in the middle of a FW update,
for example.