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

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Date:	Sun, 30 Nov 2014 15:48:15 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
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 Sunday 30 November 2014 10:00:00 Guenter Roeck wrote:
> 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.
> 

This is internal kernel function, no problem. If you prefer 
NODATA instead RANGE I will change it.

> >   #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

There was some problems when I tested similar patch for radeon.ko 
(do not report temperature to userspace when card is turned off).

I can test lm-sensors which is in Ubuntu 12.04 LTS (there is 
probably some older version) what happens with -ENODATA from i8k.

-- 
Pali Rohár
pali.rohar@...il.com

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