linux-kernel - RE: [PATCH] Input: serio: make HYPERV_KEYBOARD depend on SERIO

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Message-ID: <EE124450C0AAF944A40DD71E61F878C9920A1C@SINEX14MBXC417.southpacific.corp.microsoft.com>
Date:	Tue, 12 Aug 2014 05:51:28 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	"dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	KY Srinivasan <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH] Input: serio: make HYPERV_KEYBOARD depend on
 SERIO_I8042=y

> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> > Decoupling the dependency between hyperv_keyboard and i8042 needs
> > non-trivial efforts and is hence a long term goal.
> >
> > For now, let's make the dependency explicit so people can beware of this.
>
> You didn't make anyone "aware" of this, you just prevented people from
> being able to select the module unless they build the driver into the
> kernel, which isn't very nice.

Yes, exactly.

> What exactly needs to be done to fix this "correctly" that is going to
> take too much work at the moment?
Hi Greg,
The current implementation of hyperv-keyboard.c borrows
serio_interrupt() to pass the key strokes to the high level component.
serio_interrupt() actually depends on atkbd.c and i8042.c, so this doesn't
work for a Generation 2 hyper-v guest because no i8042 keyboard controller
is emulated: http://technet.microsoft.com/en-us/library/dn282285.aspx

To decouple the dependency between the hyperv-keyboard and i8042
modules, I suppose we probably have to re-implement hyperv-keyboard by
using input_allocate_device(), input_register_device(), and using
input_report_key() to pass the key strokes to the high level.

I'll have to need some time for further investigation and a new
implementation. Before the new code is completely ready, IMHO the
patch can help to avoid a bad user experience like Arch Linux working
as a Generation 2 hyper-v guest.

BTW, looks most of Linux distros (like RHEL, Ubuntu, SUSE) have
CONFIG_SERIO_I8042=y, probably because it's the result of
"make defconfig". So the patch actually doesn't affect these distros.

Thanks,
-- Dexuan
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