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

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Date:	Wed, 22 Jun 2016 08:53:19 +0200
From:	Michał Kępień <kernel@...pniu.pl>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Andy Lutomirski <luto@...nel.org>, Jethro <xtompok@...il.com>,
	linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Experimental PATCH] dell-smm-hwmon: Add support for disabling
 automatic BIOS fan control

> > >> Tested on a Dell XPS13 9333. Changing the value of pwm1_enable appears
> > >> to have no effect here.
> > > 
> > > Can you check what i8k_enable_fan_auto_mode() returns? Error code or not?
> > 
> > No error. However, independently on the value I set, the BIOS always
> > overrides the speed of the fan.
> 
> Ok, looks like this is model or platform specific call...
> 
> If you want, you can try to play with dellfan source code [1]. There is
> e.g. in comment specified two methods for disabling that BIOS thermal
> automode [2]. Looks like second method is that which I implemented in
> patch...
> 
> [1] - https://github.com/clopez/dellfan
> [2] - https://github.com/clopez/dellfan/blob/master/dellfan.c#L64

Pali, I played around with your patch a bit on my Vostro V131 (BIOS A04)
and the results are similar to Gabriele's:

  * I can write values 1 and 2 to pwm{1,2}_enable, which causes
    i8k_enable_fan_auto_mode() to return 0, but the desired speed set
    using pwm{1,2} is quickly overridden by the BIOS, no matter which
    thermal control mode is set,
    
  * trying to set the BIOS thermal control mode to the same value it was
    already set to causes i8k_enable_fan_auto_mode() to return -22:
    
        # echo 1 > /sys/class/hwmon/hwmon1/pwm1_enable
        # echo 1 > /sys/class/hwmon/hwmon1/pwm1_enable
        bash: echo: write error: Input/output error
        # echo 2 > /sys/class/hwmon/hwmon1/pwm2_enable
        # echo 2 > /sys/class/hwmon/hwmon1/pwm2_enable
        bash: echo: write error: Input/output error
        # echo 1 > /sys/class/hwmon/hwmon1/pwm1_enable
        # echo 2 > /sys/class/hwmon/hwmon1/pwm2_enable
        #
    
  * I tried changing I8K_SMM_MANUAL_FAN and I8K_SMM_AUTO_FAN to 0x30a3
    and 0x31a3, respectively (according to [2]), but it hasn't changed
    anything, i.e. BIOS is taking over shortly after any value is
    written to pwm{1,2}.

-- 
Best regards,
Michał Kępień