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

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Date:	Wed, 6 Apr 2011 09:19:15 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Guenter Roeck <guenter.roeck@...csson.com>
Cc:	Natarajan Gurumoorthy <natg@...gle.com>,
	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, 5 Apr 2011 20:02:20 -0700, Guenter Roeck wrote:
> On Tue, Apr 05, 2011 at 10:50:47PM -0400, Natarajan Gurumoorthy wrote:
> > Guenter,
> >       Thank you for spotting the fact the everything goes south if you
> > disable "watchdog". I am working on a solution. Looks like the ideal
> > place to store it87_io_lock.c will be drivers/misc and the IT87_LOCK
> > config will be placed before the MISC_DEVICES entry in
> > drivers/misc/Kconfig file. This will be similar to the
> > SENSORS_LIS3LV02D entry in that Kconfig file.
> > 
> Almost, only afaik that is only used inside the misc directory, or at least
> has some other components there. I don't really know how to handle this
> situation correctly, except you could of course write a mfd driver to handle
> the generic parts.
> 
> >       Now going back to the partitioning do I send this change out as
> > a multi patch set consisting of 4 parts something as below:
> > 
> > patch 0 has a description
> > 
> > patch 1 has only the lock and related files
> >         drivers/misc/Kconfig
> >         drivers/misc/Makefile
> >         include/linux/it87_lock.h
> >         drivers/misc/it87_lock.c
> > 
> > patch 2 has drivers/watchdog changes
> >         drivers/watchdog/Kconfig
> >         drivers/watchdog/it8712f_wdt.c
> >         drivers/watchdog/it87_wdt.c
> > 
> > patch 3 has drives/hwmon changes
> >         drivers/hwmon/Kconfig
> >         drivers/hwmon/it87.c
> > 
> Something like that. I have some doubts about using drivers/misc,
> but I guess you'll get feedback on that after you submit the patch set.

I would definitely prefer drivers/mfd over drivers/misc. The
problematic we are trying to solve here is typically a multi-function
device one.

This also raises concerns about the implementation. The shared spinlock
looks like a band-aid solution to me. The initial problem is that all
these drivers access I/O ports they did NOT reserve as they were
supposed to do. If they did, the conflict would have been spotted much
earlier.

I seem to recall that there has been work in the past on a new
"superio" subsystem which would help centralize detection of and I/O
access to all Super-I/O chips (bringing driver autoloading in almost
all cases as a nice side benefit.) I never had the time to review it,
but as I recall others had reviewed it so it may be in a suitable shape
for upstream inclusion (after forward-porting - the code is getting
old.)

http://www.google.com/search?q=site%3Alists.lm-sensors.org+superio+lock

Don't get me wrong, the current situation is bad enough that a band-aid
solution is welcome. But it doesn't seem good enough for the long run.

-- 
Jean Delvare
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