Re: [PATCH] Add driver to force WMI Thunderbolt controller power status

From: "Bernat, Yehezkel" <yehezkel.bernat@intel.com>
To: "mario.limonciello@dell.com" <mario.limonciello@dell.com>
Cc: "mika.westerberg@linux.intel.com"
	<mika.westerberg@linux.intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"platform-driver-x86@vger.kernel.org" 
	<platform-driver-x86@vger.kernel.org>,
	"dvhart@infradead.org" <dvhart@infradead.org>,
	"hughsient@gmail.com" <hughsient@gmail.com>
Subject: Re: [PATCH] Add driver to force WMI Thunderbolt controller power status
Date: Wed, 6 Sep 2017 19:46:14 +0000	[thread overview]
Message-ID: <1504727178.2677.158.camel@intel.com> (raw)
In-Reply-To: <1504726863.2677.154.camel@intel.com>

(Resending with a fixed CC list. Sorry.)

> 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.