linux-kernel - Re: [lm-sensors] [PATCH v5 1/2] Use "request_muxed

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Date:	Thu, 14 Apr 2011 10:58:33 -0700
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Hans de Goede <hdegoede@...hat.com>
CC:	Nat Gurumoorthy <natg@...gle.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Waychison <mikew@...gle.com>
Subject: Re: [lm-sensors] [PATCH v5 1/2] Use "request_muxed_region" in it87
 watchdog drivers

On Wed, 2011-04-13 at 02:50 -0400, Hans de Goede wrote:
> Hi,
> 
> On 04/12/2011 10:49 PM, Nat Gurumoorthy wrote:
> > 01 - Changes to it87 watchdog driver to use "request_muxed_region"
> > Serialize access to the hardware by using "request_muxed_region" macro defined
> > by Alan Cox. Call to this macro will hold off the requestor if the resource is
> > currently busy.
> >
> > The use of the above macro makes it possible to get rid of
> > spinlocks in it8712f_wdt.c and it87_wdt.c watchdog drivers.
> > This also greatly simplifies the implementation of it87_wdt.c driver.
> >
> > Signed-off-by: Nat Gurumoorthy<natg@...gle.com>
> > ---
> >
> > diff --git a/drivers/watchdog/it8712f_wdt.c b/drivers/watchdog/it8712f_wdt.c
> > index 6143f52..51bfbc0 100644
> > --- a/drivers/watchdog/it8712f_wdt.c
> > +++ b/drivers/watchdog/it8712f_wdt.c
> > @@ -51,7 +51,6 @@ MODULE_PARM_DESC(nowayout, "Disable watchdog shutdown on close");
> >
> >   static unsigned long wdt_open;
> >   static unsigned expect_close;
> > -static spinlock_t io_lock;
> >   static unsigned char revision;
> >
> >   /* Dog Food address - We use the game port address */
> > @@ -123,7 +122,11 @@ static inline void superio_select(int ldn)
> >
> >   static inline void superio_enter(void)
> >   {
> > -	spin_lock(&io_lock);
> > +	/*
> > +	 * Reserve REG and REG + 1 for exclusive access.
> > +	 */
> > +	(void) request_muxed_region(REG, 2, NAME);
> > +
> 
> You shouldn't (void) this, there is a reason you get a warning
> otherwise! request_muxed_region can still fail if some other driver
> has done a none muxed request_region on the same region, and in that
> case you should not continue with accessing the io-ports.
> 
Absolutely agree - even if that means adding a return code to
superio_enter() and checking it from the calling code.

Guenter


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