linux-kernel - Re: [PATCH v6 1/2] Use "request_muxed

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Message-ID: <BANLkTin6M0R4d+HMovbRwqthSHowUEKFow@mail.gmail.com>
Date:	Thu, 14 Apr 2011 18:18:57 -0700
From:	Natarajan Gurumoorthy <natg@...gle.com>
To:	guenter.roeck@...csson.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 v6 1/2] Use "request_muxed_region" in it87 watchdog drivers

On Thu, Apr 14, 2011 at 3:49 PM, Guenter Roeck
<guenter.roeck@...csson.com> wrote:
> This is way too complicated. Just return an error if
> request_muxed_region fails, like all other callers of
> request_muxed_region do.
>
Guenter,
      This maybe a little complicated but it is a solution that will
correctly deal with the following scenario:
      Hardware: it8712f
      cpu: Multicore
      kernel: smp
      Modules being loaded during initialization: it8712f_wtd and w83697hf

The problem is one of the cores is halfway through initializing
it8712f_wdt and another core is just starting to run the
"w83697hf_check_wdt" which is going to call "request_region" to
reserve 0x2e 0x2f region. Just after that call on the other core
it8712f_wdt_init calls it8712f_wdt_disable which calls superio_enter
which will call "request_muxed_region" for the exact same region. This
is  guaranteed to fail because as of now w83697hf is one of the many
non compliant drivers who are calling "request_region". The w83697hf
will do the probe and conclude there is no w83697hf chip in the system
and abort rest of the driver initialization. Meanwhile the it8712f_wtd
driver initialization will fail. This will be one of those
intermittent failures that make most kernel device driver writers
prematurely bald :-).

The way I have reworked the driver will survive the above scenario.

Regards
Nat

> Guenter
>
>
>

-- 
Regards
Nat Gurumoorthy AB6SJ
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