linux-kernel - Re: [PATCH v2 2/3] platform/x86: dell-wmi: add new keymap type 0x0012

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Date:   Tue, 9 Jun 2020 10:50:38 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Mario.Limonciello@...l.com
Cc:     y.linux@...itcher.com, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, mjg59@...f.ucam.org
Subject: Re: [PATCH v2 2/3] platform/x86: dell-wmi: add new keymap type 0x0012

On Tuesday 09 June 2020 00:26:45 Mario.Limonciello@...l.com wrote:
> > Mario, are you able to get some official documentation for these 0x0012
> > event types? I think it could be really useful for community so they can
> > understand and add easily new type of code and events. Because currently
> > we are just guessing what it could be. (It is sequence? Or single event?
> > Or single event with extended data? It is generic event? Or it is real
> > keypress? etc...)
> 
> It's a single event with more data in the subsequent words.  It is definitely
> not a real keypress.  It's supposed to be data that a user application would show.
> 
> Remember the way WMI works on Linux and Windows is different.  On Windows
> userland applications get the events directly.  On Linux kernel drivers get the
> events and either use it internally, pass to another kernel driver or pass to
> userland in the form of a translated event.
> 
> So on Windows the whole buffer gets looked at directly by the application and the
> application will decode it to show a translated string.
> 
> I can certainly discuss internally about our team releasing a patch to export
> all these other events.  I would like to know what interface to recommend it pass
> to userspace though, because as I said this is more than just a keycode that
> comes through in the event.  It's not useful to just do dev_info, it really should
> be something that userspace can act on and show a translated message.
> I don't think we want to add another 15 Dell specific keycodes to the kernel for the
> various events and add another 4 more when a laptop introduces another set of keys.

Which interface to use for events? That is a good question and probably
this should be bring to the linux-input mailinglist. I think that
linux-input maintainers could have idea how to do it properly. We need
some interface which would be general enough and usable also by other
drivers / components and I'm sure that ACPI/WMI is not the only
subsystem which needs to send events from kernel to userspace.