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

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Date:	Thu, 2 Jun 2016 15:09:51 +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 Monday 30 May 2016 17:26:36 Gabriele Mazzotta wrote:
> On 30/05/2016 11:32, Pali Rohár wrote:
> > 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?
> 
> 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 Rohár
pali.rohar@...il.com