Re: [char-misc-next, v4, 5/7] watchdog: mei_wdt: register wd device only if required

From: Guenter Roeck
Date: Sun Jan 17 2016 - 16:47:28 EST

On 01/17/2016 12:54 PM, Winkler, Tomas wrote:

-----Original Message-----
From: Guenter Roeck [mailto:linux@xxxxxxxxxxxx]
Sent: Sunday, January 17, 2016 19:13
To: Winkler, Tomas
Cc: Greg Kroah-Hartman; Wim Van Sebroeck; Usyskin, Alexander; linux-
watchdog@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [char-misc-next, v4, 5/7] watchdog: mei_wdt: register wd device only
if required

Hi Tomas,

On Fri, Jan 08, 2016 at 12:49:25AM +0200, Winkler, Tomas wrote:
From: Alexander Usyskin <alexander.usyskin@xxxxxxxxx>

For Intel Broadwell and newer platforms, the ME device can inform
the host whether the watchdog functionality is activated or not.
If the watchdog functionality is not activated then the watchdog interface
can be not registered and eliminate unnecessary pings and hence lower the
power consumption by avoiding waking up the device.
The feature can be deactivated also without reboot
in that case the watchdog device should be unregistered at runtime.

Signed-off-by: Alexander Usyskin <alexander.usyskin@xxxxxxxxx>
Signed-off-by: Tomas Winkler <tomas.winkler@xxxxxxxxx>
V2: rework unregistration
V3: rebase; implement unregistraion also at runtime
V4: Rebase the code over patchset : "watchdog: Replace driver based

drivers/watchdog/mei_wdt.c | 196
1 file changed, 187 insertions(+), 9 deletions(-)

diff --git a/drivers/watchdog/mei_wdt.c b/drivers/watchdog/mei_wdt.c
index e7e3f144f2b0..85b27fc5d4ec 100644
--- a/drivers/watchdog/mei_wdt.c
+++ b/drivers/watchdog/mei_wdt.c

[ ... ]

+static void mei_wdt_unregister_work(struct work_struct *work)
+ struct mei_wdt *wdt = container_of(work, struct mei_wdt, unregister);
+ mei_wdt_unregister(wdt);

Registration is synchronous, unregistration is asynchronous.

Assuming that is on purpose, I think it warrants an explanation.

The unregistration is detected on response from the ping, which is run under same mutex as unregistration.

And that explains why registration can be synchronous and unregistration
has to be asynchronous ?