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

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Message-ID: <PU1P153MB01699917C92952BAD6B7A1E1BF7E0@PU1P153MB0169.APCP153.PROD.OUTLOOK.COM>
Date:   Tue, 5 Nov 2019 05:43:04 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>
Subject: RE: [PATCH] Input: hyperv-keyboard: Add the support of hibernation

> From: dmitry.torokhov@...il.com <dmitry.torokhov@...il.com>
> Sent: Thursday, October 3, 2019 10:46 AM
> ... 
> Right. I think in practice the current suspend implementation can work
> as freeze() for the HV keyboard, because in suspend you shut off vmbus
> channel, so there should not be wakeup signals anymore. What you do not
> want is to have the current resume to be used in place of thaw(), as
> there you re-enable the vmbus channel and resume sending wakeup requests
> as you are writing out the hibernation image to storage.
> 
> I think if vmbus allowed HV keyboard driver to supply empty thaw() and
> poweroff() implementations, while using suspend() as freeze() and
> resume() as restore(), it would solve the issue for you.
> 
> Dmitry

BTW, IMO thaw() should not be empty, because drivers/base/power/main.c: 
pm_op() uses ops->thaw for both PM_EVENT_THAW and PM_EVENT_RECOVER.

PMSG_RECOVER is the same as PM_EVENT_RECOVER.

If some step in hibernation_snapshot() -> create_image() fails, we call 
dpm_resume_start(PMSG_RECOVER) at the end of create_image(), and call
dpm_resume() in hibernation_snapshot(). An empty thaw() can not bring the
device back to normal.

Thanks,
-- Dexuan