Re: [Experimental PATCH] dell-smm-hwmon: Add support for disabling automatic BIOS fan control

["Pali Rohár" <pali.rohar@gmail.com>]

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On Sunday 22 May 2016 17:04:16 Guenter Roeck wrote:
> On 05/22/2016 04:50 AM, Pali Rohár wrote:
> > This patch exports standard hwmon pwmX_enable sysfs attribute for
> > enabling or disabling automatic fan control by BIOS. Standard
> > value "1" is for disabling automatic BIOS fan control and value
> > "2" for enabling.
> > 
> > Currently there is no way to check if BIOS auto mode is enabled (at
> > least it is not know how to do it), so hwmon sysfs attribute is
> > write-only.
> 
> You could cache the mode and report it after it was set, and define
> '0' as read value for 'unknown'.

I was thinking about it, but there is problem, that userspace can also 
update/change BIOS auto mode. Process with CAP_SYS_RAWIO can use 
sys_iopl(3) or sys_ioperm() which allows it access to I/O ports. There 
are already different i8k* userspace tools which do that. And once 
userspace change BIOS auto mode, then cached value in kernel does not 
have to be correct and can confuse other applications which use standard 
hwmon interface (not direct I/O ports).

And value '0' is already defined in hwmon API as:
"no fan speed control (i.e. fan at full speed)"

> > By default BIOS auto mode is enabled by laptop firmware.
> > 
> > When BIOS auto mode is enabled, custom fan speed value (set via
> > hwmon pwmX sysfs attribute) is overwritten by SMM in few seconds
> > and therefore any custom settings are without effect. So this is
> > reason why implementing option for disabling BIOS auto mode is
> > needed.
> > 
> > So finally this patch allows kernel to set and control fan speed on
> > laptops, but it can be dangerous (like setting speed of other
> > fans).
> > 
> > This new feature is highly experimental, uses Dell SMM calls, so
> > does not have to be supported by all laptops BIOSes. It was tested
> > on Dell Latitude E6440 with BIOS A5.
> > 
> > Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
> > ---
> > 
> >   drivers/hwmon/dell-smm-hwmon.c |   64
> >   ++++++++++++++++++++++++++++++++++------ 1 file changed, 55
> >   insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/hwmon/dell-smm-hwmon.c
> > b/drivers/hwmon/dell-smm-hwmon.c index 8a66a42..7b5144a 100644
> > --- a/drivers/hwmon/dell-smm-hwmon.c
> > +++ b/drivers/hwmon/dell-smm-hwmon.c
> > @@ -45,6 +45,8 @@
> > 
> >   #define I8K_SMM_GET_SPEED	0x02a3
> >   #define I8K_SMM_GET_FAN_TYPE	0x03a3
> >   #define I8K_SMM_GET_NOM_SPEED	0x04a3
> > 
> > +#define I8K_SMM_MANUAL_FAN	0x34a3
> > +#define I8K_SMM_AUTO_FAN	0x35a3
> > 
> >   #define I8K_SMM_GET_TEMP	0x10a3
> >   #define I8K_SMM_GET_TEMP_TYPE	0x11a3
> >   #define I8K_SMM_GET_DELL_SIG1	0xfea3
> > 
> > @@ -284,6 +286,17 @@ static int i8k_get_fan_nominal_speed(int fan,
> > int speed)
> > 
> >   }
> >   
> >   /*
> > 
> > + * Enable or disable automatic BIOS fan control support
> > + */
> > +static int i8k_enable_fan_auto_mode(bool enable)
> > +{
> > +	struct smm_regs regs = { };
> > +
> > +	regs.eax = enable ? I8K_SMM_AUTO_FAN : I8K_SMM_MANUAL_FAN;
> > +	return i8k_smm(&regs);
> > +}
> > +
> > +/*
> > 
> >    * Set the fan speed (off, low, high). Returns the new fan
> >    status. */
> >   
> >   static int i8k_set_fan(int fan, int speed)
> > 
> > @@ -702,6 +715,30 @@ static ssize_t i8k_hwmon_set_pwm(struct device
> > *dev,
> > 
> >   	return err < 0 ? -EIO : count;
> >   
> >   }
> > 
> > +static ssize_t i8k_hwmon_set_pwm_enable(struct device *dev,
> > +					struct device_attribute *attr,
> > +					const char *buf, size_t count)
> > +{
> > +	int err;
> > +	bool enable;
> > +	unsigned long val;
> > +
> > +	err = kstrtoul(buf, 10, &val);
> > +	if (err)
> > +		return err;
> > +
> > +	if (val == 0)
> > +		return -EINVAL;
> > +
> > +	enable = (val != 1);
> > +
> 
> Please accepted only explicit values (1 and 2).

In Documentation/hwmon/sysfs-interface is written:

pwm[1-*]_enable
		2+: automatic fan speed control enabled

And this reason why my patch accept also other numeric values.

If other values does not make sense, maybe update documentation file?

> Thanks,
> Guenter
> 
> > +	mutex_lock(&i8k_mutex);
> > +	err = i8k_enable_fan_auto_mode(enable);
> > +	mutex_unlock(&i8k_mutex);
> > +
> > +	return err ? -EIO : count;
> > +}
> > +
> > 
> >   static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
> >   i8k_hwmon_show_temp, NULL, 0); static
> >   SENSOR_DEVICE_ATTR(temp1_label, S_IRUGO,
> >   i8k_hwmon_show_temp_label, NULL,
> >   
> >   			  0);
> > 
> > @@ -719,18 +756,24 @@ static SENSOR_DEVICE_ATTR(fan1_label,
> > S_IRUGO, i8k_hwmon_show_fan_label, NULL,
> > 
> >   			  0);
> >   
> >   static SENSOR_DEVICE_ATTR(pwm1, S_IRUGO | S_IWUSR,
> >   i8k_hwmon_show_pwm,
> >   
> >   			  i8k_hwmon_set_pwm, 0);
> > 
> > +static SENSOR_DEVICE_ATTR(pwm1_enable, S_IWUSR, NULL,
> > i8k_hwmon_set_pwm_enable, +			  0);
> > 
> >   static SENSOR_DEVICE_ATTR(fan2_input, S_IRUGO,
> >   i8k_hwmon_show_fan, NULL,
> >   
> >   			  1);
> >   
> >   static SENSOR_DEVICE_ATTR(fan2_label, S_IRUGO,
> >   i8k_hwmon_show_fan_label, NULL,
> >   
> >   			  1);
> >   
> >   static SENSOR_DEVICE_ATTR(pwm2, S_IRUGO | S_IWUSR,
> >   i8k_hwmon_show_pwm,
> >   
> >   			  i8k_hwmon_set_pwm, 1);
> > 
> > +static SENSOR_DEVICE_ATTR(pwm2_enable, S_IWUSR, NULL,
> > i8k_hwmon_set_pwm_enable, +			  1);
> > 
> >   static SENSOR_DEVICE_ATTR(fan3_input, S_IRUGO,
> >   i8k_hwmon_show_fan, NULL,
> >   
> >   			  2);
> >   
> >   static SENSOR_DEVICE_ATTR(fan3_label, S_IRUGO,
> >   i8k_hwmon_show_fan_label, NULL,
> >   
> >   			  2);
> >   
> >   static SENSOR_DEVICE_ATTR(pwm3, S_IRUGO | S_IWUSR,
> >   i8k_hwmon_show_pwm,
> >   
> >   			  i8k_hwmon_set_pwm, 2);
> > 
> > +static SENSOR_DEVICE_ATTR(pwm3_enable, S_IWUSR, NULL,
> > i8k_hwmon_set_pwm_enable, +			  2);
> > 
> >   static struct attribute *i8k_attrs[] = {
> >   
> >   	&sensor_dev_attr_temp1_input.dev_attr.attr,	/* 0 */
> > 
> > @@ -744,12 +787,15 @@ static struct attribute *i8k_attrs[] = {
> > 
> >   	&sensor_dev_attr_fan1_input.dev_attr.attr,	/* 8 */
> >   	&sensor_dev_attr_fan1_label.dev_attr.attr,	/* 9 */
> >   	&sensor_dev_attr_pwm1.dev_attr.attr,		/* 10 */
> > 
> > -	&sensor_dev_attr_fan2_input.dev_attr.attr,	/* 11 */
> > -	&sensor_dev_attr_fan2_label.dev_attr.attr,	/* 12 */
> > -	&sensor_dev_attr_pwm2.dev_attr.attr,		/* 13 */
> > -	&sensor_dev_attr_fan3_input.dev_attr.attr,	/* 14 */
> > -	&sensor_dev_attr_fan3_label.dev_attr.attr,	/* 15 */
> > -	&sensor_dev_attr_pwm3.dev_attr.attr,		/* 16 */
> > +	&sensor_dev_attr_pwm1_enable.dev_attr.attr,	/* 11 */
> > +	&sensor_dev_attr_fan2_input.dev_attr.attr,	/* 12 */
> > +	&sensor_dev_attr_fan2_label.dev_attr.attr,	/* 13 */
> > +	&sensor_dev_attr_pwm2.dev_attr.attr,		/* 14 */
> > +	&sensor_dev_attr_pwm2_enable.dev_attr.attr,	/* 15 */
> > +	&sensor_dev_attr_fan3_input.dev_attr.attr,	/* 16 */
> > +	&sensor_dev_attr_fan3_label.dev_attr.attr,	/* 17 */
> > +	&sensor_dev_attr_pwm3.dev_attr.attr,		/* 18 */
> > +	&sensor_dev_attr_pwm3_enable.dev_attr.attr,	/* 19 */
> > 
> >   	NULL
> >   
> >   };
> > 
> > @@ -768,13 +814,13 @@ static umode_t i8k_is_visible(struct kobject
> > *kobj, struct attribute *attr,
> > 
> >   	if (index >= 6 && index <= 7 &&
> >   	
> >   	    !(i8k_hwmon_flags & I8K_HWMON_HAVE_TEMP4))
> >   		
> >   		return 0;
> > 
> > -	if (index >= 8 && index <= 10 &&
> > +	if (index >= 8 && index <= 11 &&
> > 
> >   	    !(i8k_hwmon_flags & I8K_HWMON_HAVE_FAN1))
> >   		
> >   		return 0;
> > 
> > -	if (index >= 11 && index <= 13 &&
> > +	if (index >= 12 && index <= 15 &&
> > 
> >   	    !(i8k_hwmon_flags & I8K_HWMON_HAVE_FAN2))
> >   		
> >   		return 0;
> > 
> > -	if (index >= 14 && index <= 16 &&
> > +	if (index >= 16 && index <= 19 &&
> > 
> >   	    !(i8k_hwmon_flags & I8K_HWMON_HAVE_FAN3))
> >   		
> >   		return 0;

-- 
Pali Rohár
pali.rohar@gmail.com

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