linux-kernel - Re: [PATCH] dell-smm-hwmon: Cache fan_type() calls and use fan

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Date:	Sun, 22 May 2016 02:28:00 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Jan C Peters <jcpeters89@...il.com>,
	Thorsten Leemhuis <fedora@...mhuis.info>,
	David Santamaría Rogado <howl.nsp@...il.com>,
	Peter Saunderson <peteasa@...il.com>,
	Jean Delvare <jdelvare@...e.com>,
	Tolga Cakir <cevelnet@...il.com>, linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dell-smm-hwmon: Cache fan_type() calls and use fan_status() for fan detection

On Sunday 22 May 2016 02:19:48 Guenter Roeck wrote:
> On 05/21/2016 07:46 AM, Pali Rohár wrote:
> > On more Dell machines (e.g. Dell Precision M3800)
> > I8K_SMM_GET_FAN_TYPE call is too expensive (CPU is too long in SMM
> > mode) and cause kernel to hang. This patch cache type for each fan
> > (as it should not change) and change the way how fan presense is
> > detected. It revert and use function fan_status() as was before
> > commit f989e55452c7 ("i8k: Add support for fan labels").
> > 
> > Moreover, kernel hangs for 2 - 3 seconds only sometimes and only on
> > some Dell machines. When kernel hangs fan speed is at max. So it
> > was hard to debug and bisect where is root of this problem. It
> > looks like this is bug in Dell BIOS which implement fan type SMM
> > code... and there is no way how to fix it in kernel.
> > 
> > Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> > Reviewed-by: Jean Delvare <jdelvare@...e.de>
> > Reported-and-tested-by: Tolga Cakir <cevelnet@...il.com>
> > Fixes: f989e55452c7 ("i8k: Add support for fan labels")
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=112021
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=100121
> > Cc: stable@...r.kernel.org # v4.0+, will need backport
> 
> Should this patch be applied, or do you wait for more testing ?

I would like to hear some confirmation from people with affected machine.

> Guenter
> 
> > ---
> > 
> >   drivers/hwmon/dell-smm-hwmon.c |   21 ++++++++++++++++-----
> >   1 file changed, 16 insertions(+), 5 deletions(-)
> > 
> > ---
> > 
> > Hi!
> > 
> > Jan C Peters, Thorsten Leemhuis, David Santamaría Rogado, Peter
> > Saunderson and others, can you test this patch if it fixes your
> > freeze problem at boottime and when using "sensors" program?
> > 
> > I need to know if this patch fixes problem on Dell Studio XPS 8000
> > and Dell Studio XPS 8100 machines, so we can revert git commits:
> > 
> > 6220f4ebd7b4 ("hwmon: (dell-smm) Blacklist Dell Studio XPS 8000")
> > a4b45b25f18d ("hwmon: (dell-smm) Blacklist Dell Studio XPS 8100")
> > 
> > diff --git a/drivers/hwmon/dell-smm-hwmon.c
> > b/drivers/hwmon/dell-smm-hwmon.c index c43318d..577445f 100644
> > --- a/drivers/hwmon/dell-smm-hwmon.c
> > +++ b/drivers/hwmon/dell-smm-hwmon.c
> > @@ -235,7 +235,7 @@ static int i8k_get_fan_speed(int fan)
> > 
> >   /*
> >   
> >    * Read the fan type.
> >    */
> > 
> > -static int i8k_get_fan_type(int fan)
> > +static int _i8k_get_fan_type(int fan)
> > 
> >   {
> >   
> >   	struct smm_regs regs = { .eax = I8K_SMM_GET_FAN_TYPE, };
> > 
> > @@ -243,6 +243,17 @@ static int i8k_get_fan_type(int fan)
> > 
> >   	return i8k_smm(&regs) ? : regs.eax & 0xff;
> >   
> >   }
> > 
> > +static int i8k_get_fan_type(int fan)
> > +{
> > +	/* I8K_SMM_GET_FAN_TYPE SMM call is expensive, so cache values */
> > +	static int types[2] = { INT_MIN, INT_MIN };
> > +
> > +	if (types[fan] == INT_MIN)
> > +		types[fan] = _i8k_get_fan_type(fan);
> > +
> > +	return types[fan];
> > +}
> > +
> > 
> >   /*
> >   
> >    * Read the fan nominal rpm for specific fan speed.
> >    */
> > 
> > @@ -767,13 +778,13 @@ static int __init i8k_init_hwmon(void)
> > 
> >   	if (err >= 0)
> >   	
> >   		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP4;
> > 
> > -	/* First fan attributes, if fan type is OK */
> > -	err = i8k_get_fan_type(0);
> > +	/* First fan attributes, if fan status is OK */
> > +	err = i8k_get_fan_status(0);
> > 
> >   	if (err >= 0)
> >   	
> >   		i8k_hwmon_flags |= I8K_HWMON_HAVE_FAN1;
> > 
> > -	/* Second fan attributes, if fan type is OK */
> > -	err = i8k_get_fan_type(1);
> > +	/* Second fan attributes, if fan status is OK */
> > +	err = i8k_get_fan_status(1);
> > 
> >   	if (err >= 0)
> >   	
> >   		i8k_hwmon_flags |= I8K_HWMON_HAVE_FAN2;


-- 
Pali Rohár
pali.rohar@...il.com

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