linux-kernel - Re: [PATCH] i8k: Fix temperature bug handling in i8k_get

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Date:	Sat, 29 Nov 2014 16:12:07 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Honeyman <stevenhoneyman@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i8k: Fix temperature bug handling in i8k_get_temp()

On Tue, Nov 18, 2014 at 03:56:54PM +0100, Pali Rohár wrote:
> Static array prev[] was incorrectly initialized. It should be initialized to
> some "invalid" temperature value (above I8K_MAX_TEMP).
> 
> Next, function should store "invalid" value to prev[] (above I8K_MAX_TEMP),
> not valid (= I8K_MAX_TEMP) because whole temperature bug handling will not
> work.
> 
> And last part, to not break existing detection of temperature sensors, register
> them also if i8k report too high temperature (above I8K_MAX_TEMP). This is
> needed because some sensors are sometimes turned off (e.g sensor on GPU which
> can be turned off/on) and in this case SMM report too high value.
> 
> To prevent reporting "invalid" values to userspace, return -EINVAL. In this case
> sensors which are currently turned off (e.g optimus/powerexpress/enduro gpu)
> are reported as "N/A" by lm-sensors package.
> 
> Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> ---
>  drivers/char/i8k.c |   16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
> index 7272b08..e34a019 100644
> --- a/drivers/char/i8k.c
> +++ b/drivers/char/i8k.c
> @@ -298,7 +298,7 @@ static int i8k_get_temp(int sensor)
>  	int temp;
>  
>  #ifdef I8K_TEMPERATURE_BUG
> -	static int prev[4];
> +	static int prev[4] = { I8K_MAX_TEMP+1, I8K_MAX_TEMP+1, I8K_MAX_TEMP+1, I8K_MAX_TEMP+1 };

This results in a checkpatch warning. Please split, and add a space before
and after '+'. Actually, I would suggest to use something something like

#define I8K_INVALID_TEMP	(I8K_MAX_TEMP + 1)

and to use it instead of hard-coding "I8K_MAX_TEMP + 1" in the code.

>  #endif
>  	regs.ebx = sensor & 0xff;
>  	rc = i8k_smm(&regs);
> @@ -317,10 +317,12 @@ static int i8k_get_temp(int sensor)
>  	 */
>  	if (temp > I8K_MAX_TEMP) {
>  		temp = prev[sensor];
> -		prev[sensor] = I8K_MAX_TEMP;
> +		prev[sensor] = I8K_MAX_TEMP+1;
>  	} else {
>  		prev[sensor] = temp;
>  	}
> +	if (temp > I8K_MAX_TEMP)
> +		return -ERANGE;
>  #endif
>  
>  	return temp;
> @@ -499,6 +501,8 @@ static ssize_t i8k_hwmon_show_temp(struct device *dev,
>  	int temp;
>  
>  	temp = i8k_get_temp(index);
> +	if (temp == -ERANGE)
> +		return -EINVAL;
>  	if (temp < 0)
>  		return temp;
>  	return sprintf(buf, "%d\n", temp * 1000);
> @@ -610,17 +614,17 @@ static int __init i8k_init_hwmon(void)
>  
>  	/* CPU temperature attributes, if temperature reading is OK */
>  	err = i8k_get_temp(0);
> -	if (err >= 0)
> +	if (err >= 0 || err == -ERANGE)
>  		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP1;
>  	/* check for additional temperature sensors */
>  	err = i8k_get_temp(1);
> -	if (err >= 0)
> +	if (err >= 0 || err == -ERANGE)
>  		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP2;
>  	err = i8k_get_temp(2);
> -	if (err >= 0)
> +	if (err >= 0 || err == -ERANGE)
>  		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP3;
>  	err = i8k_get_temp(3);
> -	if (err >= 0)
> +	if (err >= 0 || err == -ERANGE)
>  		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP4;
>  
>  	/* Left fan attributes, if left fan is present */
> -- 
> 1.7.9.5
> 
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