linux-kernel - Re: [PATCH] applesmc: Bump max wait and rearrange udelay

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Message-ID: <20120915225841.GA3816@roeck-us.net>
Date:	Sat, 15 Sep 2012 15:58:41 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Parag Warudkar <parag.lkml@...il.com>
Cc:	lm-sensors@...sensors.org, linux-kernel@...r.kernel.org,
	rydberg@...omail.se, khali@...ux-fr.org
Subject: Re: [PATCH] applesmc: Bump max wait and rearrange udelay

On Sat, Sep 15, 2012 at 06:42:30PM -0400, Parag Warudkar wrote:
> I have been getting a steady stream of wait_read timeouts on my 2010 MBP.
> 
> After playing around with various values of APPLESMC_MAX_WAIT a value of 
> 0x10000 reduces the wait_read failures to zero under most normal workloads 
> - with and without AC power plugged in, at idle and and at make -j4 loads.
> 
> While there I noticed we don't really need to udelay before first inb() - 
> so I moved it down to after first and subsequent failures.
> 
> Been running this for couple days without any issues.
> 
> Signed-off-by: Parag Warudkar <parag.lkml@...il.com>
> 
> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
> index 2827088..46cb458 100644
> --- a/drivers/hwmon/applesmc.c
> +++ b/drivers/hwmon/applesmc.c
> @@ -56,7 +56,7 @@
>  /* wait up to 32 ms for a status change. */
>  #define APPLESMC_MIN_WAIT	0x0010
>  #define APPLESMC_RETRY_WAIT	0x0100
> -#define APPLESMC_MAX_WAIT	0x8000
> +#define APPLESMC_MAX_WAIT	0x10000
>  
>  #define APPLESMC_READ_CMD	0x10
>  #define APPLESMC_WRITE_CMD	0x11
> @@ -170,11 +170,11 @@ static int wait_read(void)
>  	u8 status;
>  	int us;
>  	for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {

I wonder if it would make sense to keep APPLESMC_MAX_WAIT as it is now
and replace the loop termination conditions with
				us <= APPLESMC_MAX_WAIT

That would accomplish the same, and APPLESMC_MAX_WAIT would reflect
the real maximum wait time.

Also, since the delay time can get quite large, would it make sense to replace
udelay with usleep_range() ?

Guenter

> -		udelay(us);
>  		status = inb(APPLESMC_CMD_PORT);
>  		/* read: wait for smc to settle */
>  		if (status & 0x01)
>  			return 0;
> +		udelay(us);
>  	}
>  
>  	pr_warn("wait_read() fail: 0x%02x\n", status);
> @@ -192,11 +192,12 @@ static int send_byte(u8 cmd, u16 port)
>  
>  	outb(cmd, port);
>  	for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
> -		udelay(us);
>  		status = inb(APPLESMC_CMD_PORT);
>  		/* write: wait for smc to settle */
> -		if (status & 0x02)
> +		if (status & 0x02) {
> +			udelay(us);
>  			continue;
> +		}
>  		/* ready: cmd accepted, return */
>  		if (status & 0x04)
>  			return 0;
> 
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