linux-kernel - Re: [PATCH] Make all it87 drivers SMP safe.

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Message-ID: <20110406004312.GA21882@ericsson.com>
Date:	Tue, 5 Apr 2011 17:43:12 -0700
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Natarajan Gurumoorthy <natg@...gle.com>
CC:	Jean Delvare <khali@...ux-fr.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Mike Waychison <mikew@...gle.com>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>
Subject: Re: [PATCH] Make all it87 drivers SMP safe.

On Tue, Apr 05, 2011 at 08:13:50PM -0400, Natarajan Gurumoorthy wrote:
> Guenter,
>       How would you partition it out? Are you suggesting that we do
> the following:
> 
> Patch1:
>    drivers/hwmon/Kconfig          |    1 +
>    drivers/hwmon/it87.c           |   14 ++++++++++++-
> 
> Patch2:
>    drivers/watchdog/Kconfig       |   12 +++++++++++
>    drivers/watchdog/Makefile      |    1 +
>    drivers/watchdog/it8712f_wdt.c |   10 ++++----
>    drivers/watchdog/it87_lock.c   |   27 +++++++++++++++++++++++++
>    drivers/watchdog/it87_wdt.c    |   42 ++++++---------------------------------
> 
> Patch3:
>    include/linux/it87_lock.h      |   28 ++++++++++++++++++++++++++
> 
No, not really. The include file is part of the locking code, and the sequence is wrong.

I personally would introduce the lock in the 1st patch.
This would affect
	drivers/watchdog/it87_lock.c
	include/linux/it87_lock.h
	drivers/watchdog/Makefile
	drivers/watchdog/Kconfig

The second patch would update the watchdog driver, affecting 
	drivers/watchdog/Kconfig
	drivers/watchdog/it8712f_wdt.c

and the last patch would update the hwmon driver.
	drivers/hwmon/Kconfig
	drivers/hwmon/it87.c

Others may argue that patch 1 and 2 (introducing the lock and updating
the watchdog driver) should be in a single patch, since the lock alone
does not do anything without being used. This is a matter of opinion
and really depends on the maintainer of the watchdog subsystem.

Note that your patch has practical problems. If I disable WATCHDOG but enable
the IT87 hwmon driver, I get:

warning: (SENSORS_IT87) selects IT87_LOCK which has unmet direct dependencies (WATCHDOG)

during configuration, and undefined references to it87_io_lock when linking.
So it looks like you might want to consider moving the locking code to a location
outside the watchdog code.
 
Thanks,
Guenter
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