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

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Message-ID: <20160530093204.GR29844@pali>
Date:	Mon, 30 May 2016 11:32:04 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Gabriele Mazzotta <gabriele.mzt@...il.com>
Cc:	Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Michał Kępień <kernel@...pniu.pl>,
	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

On Friday 27 May 2016 14:11:11 Gabriele Mazzotta wrote:
> On 22/05/2016 13:50, 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.
> > 
> > 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.
> 
> 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?

-- 
Pali Rohár
pali.rohar@...il.com