linux-kernel - Re: [PATCH v3] Add driver to force WMI Thunderbolt controller power status

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Message-ID: <20170914091416.GA28049@wunner.de>
Date:   Thu, 14 Sep 2017 11:14:16 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Mario.Limonciello@...l.com
Cc:     dvhart@...radead.org, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, hughsient@...il.com,
        yehezkelshb@...il.com, mika.westerberg@...ux.intel.com
Subject: Re: [PATCH v3] Add driver to force WMI Thunderbolt controller power
 status

On Thu, Sep 14, 2017 at 06:42:03AM +0000, Mario.Limonciello@...l.com wrote:
> > On Fri, Sep 08, 2017 at 10:23:11AM -0500, Mario Limonciello wrote:
> > > +static const struct wmi_device_id intel_wmi_thunderbolt_id_table[] = {
> > > +	{ .guid_string = INTEL_WMI_THUNDERBOLT_GUID },
> > > +	{ },
> > > +};
> > 
> > I'm not familiar with WMI, but don't you need a MODULE_DEVICE_TABLE here?
> > How does user space know which module to load upon receiving the uevent?
> 
> Some macros for WMI bus devices.
> https://github.com/torvalds/linux/blob/e0f25a3f2d052e36ff67a9b4db835c3e27e950d8/include/linux/wmi.h#L55
> https://github.com/torvalds/linux/blob/master/include/linux/device.h#L1487

No, the init and exit hooks defined by this macro are executed
*after* the module has been loaded.  The question was, how does
the module get loaded in the first place?

Looking at drivers/platform/x86/wmi.c:wmi_dev_uevent() it seems that
a modalias consisting of "wmi:" followed by the GUID is sent to udevd.
For udevd to then load the module, I suspect you need to add a
MODULE_DEVICE_TABLE(wmi, ...) to your driver.

Thanks,

Lukas