RE: [PATCH] Input: hyperv-keyboard: Add the support of hibernation

[Dexuan Cui <decui@microsoft.com>]

> From: dmitry.torokhov@gmail.com <dmitry.torokhov@gmail.com>
> Sent: Thursday, September 19, 2019 9:18 AM
> 
> Hi Dexuan,
> 
> On Wed, Sep 11, 2019 at 11:36:20PM +0000, Dexuan Cui wrote:
> > We need hv_kbd_pm_notify() to make sure the pm_wakeup_hard_event()
> call
> > does not prevent the system from entering hibernation: the hibernation
> > is a relatively long process, which can be aborted by the call
> > pm_wakeup_hard_event(), which is invoked upon keyboard events.
> >
> > diff --git a/drivers/input/serio/hyperv-keyboard.c
> b/drivers/input/serio/hyperv-keyboard.c
> > index 88ae7c2..277dc4c 100644
> > --- a/drivers/input/serio/hyperv-keyboard.c
> > +++ b/drivers/input/serio/hyperv-keyboard.c
> > @@ -10,6 +10,7 @@
> >  #include <linux/hyperv.h>
> >  #include <linux/serio.h>
> >  #include <linux/slab.h>
> > +#include <linux/suspend.h>
> >
> >  /*
> >   * Current version 1.0
> > @@ -95,6 +96,9 @@ struct hv_kbd_dev {
> >  	struct completion wait_event;
> >  	spinlock_t lock; /* protects 'started' field */
> >  	bool started;
> > +
> > +	struct notifier_block pm_nb;
> > +	bool hibernation_in_progress;
> 
> Why do you use notifier block instead of exposing proper PM methods if
> you want to support hibernation?
> 
> Dmitry

Hi,
In the patch I do implement hv_kbd_suspend() and hv_kbd_resume(), and
add them into the hv_kbd_drv struct:

@@ -416,6 +472,8 @@ static struct  hv_driver hv_kbd_drv = {
        .id_table = id_table,
        .probe = hv_kbd_probe,
        .remove = hv_kbd_remove,
+       .suspend = hv_kbd_suspend,
+       .resume = hv_kbd_resume,

The .suspend and .resume callbacks are inroduced by another patch (which
uses the dev_pm_ops struct):
271b2224d42f ("Drivers: hv: vmbus: Implement suspend/resume for VSC drivers for hibernation")
(which is on the Hyper-V tree's hyperv-next branch:
https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/commit/?h=hyperv-next&id=271b2224d42f88870e6b060924ee374871c131fc )

The only purpose of the notifier is to set the variable 
kbd_dev->hibernation_in_progress to true during the hibernation process.

As I explained in the changelog, the hibernation is a long process (which
can take 10+ seconds), during which the user may unintentionally touch
the keyboard, causing key up/down events, which are still handled by
hv_kbd_on_receive(), which calls pm_wakeup_hard_event(), which
calls some other functions which increase the global counter
"pm_abort_suspend", and hence pm_wakeup_pending() becomes true.

pm_wakeup_pending() is tested in a lot of places in the suspend
process and eventually an unintentional keystroke (or mouse movement,
when it comes to the Hyper-V mouse driver drivers/hid/hid-hyperv.c)
causes the whole hibernation process to be aborted. Usually this
behavior is not expected by the user, I think.

So, I use the notifier to set the flag variable and with it the driver can
know when it should not call pm_wakeup_hard_event().

Thanks,
-- Dexuan