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

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Message-ID: <547ADC90.8000507@roeck-us.net>
Date:	Sun, 30 Nov 2014 01:00:00 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Pali Rohár <pali.rohar@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Steven Honeyman <stevenhoneyman@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i8k: Fix temperature bug handling in i8k_get_temp()

On 11/18/2014 06:56 AM, 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 };
>   #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;

Can we return -ENODATA in this case ? I think that would be more appropriate.

>   #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;

and can we also return -ENODATA to user space ?
This would make the code a bit cleaner.

Thanks,
Guenter

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