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

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Date:	Thu, 14 Apr 2011 15:49:30 -0700
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Nat 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 v6 1/2] Use "request_muxed_region" in it87 watchdog
 drivers

On Thu, 2011-04-14 at 17:37 -0400, 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 first call to request_muxed_region will attempt 10 times 
> to reserve the region before it gives up. This will typically get called from
> the driver init routines. If this succeeds then subsequent calls wait forever
> for the resource to be available.
> 
> 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..8bf2524 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 */
> @@ -121,9 +120,46 @@ static inline void superio_select(int ldn)
>  	outb(ldn, VAL);
>  }
>  
> -static inline void superio_enter(void)
> +static inline int
> +try_superio_enter(void)
>  {
> -	spin_lock(&io_lock);
> +	int num_tries = 10;
> +	/*
> +	 * Try to reserve REG and REG + 1 for exclusive access.
> +	 * Give up after 10 attempts.
> +	 */
> +	while (num_tries--) {
> +		if (!request_muxed_region(REG, 2, NAME)) {
> +			if (num_tries)
> +				continue;
> +
> +			/*
> +			 * Someone is holding the region. Give up.
> +			 */
> +			pr_err("I/O address 0x%04x already in use\n", REG);
> +			return -EBUSY;
> +		}
> +
> +		break;
> +	}
> +
This is way too complicated. Just return an error if
request_muxed_region fails, like all other callers of
request_muxed_region do.

Guenter


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