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Re: [PATCH] dell-smm-hwmon: Cache fan_type() calls and use fan_status() for fan detection

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  Re: [PATCH] dell-smm-hwmon: Cache fan_type() calls and use fan_status() for fan detection Pali Rohár <pali.rohar@gmail.com> - 2016-06-13 20:40 +0200

#1421110 — Re: [PATCH] dell-smm-hwmon: Cache fan_type() calls and use fan_status() for fan detection

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On Monday 30 May 2016 13:45:51 Thorsten Leemhuis wrote:
> Pali Rohár wrote on 27.05.2016 15:21:
> > On Friday 27 May 2016 15:05:54 Thorsten Leemhuis wrote:
> >> Pali Rohár wrote on 27.05.2016 12:45:
> >> So I tried a few things
> >> and came to the conclusion: the problem shows up as soon as
> >> i8k_get_fan_type() (introduced in f989e55452) is called somewhere.
> > 
> > So, once kernel call i8k_get_fan_type() function, then fan speed
> > going up/down?
> 
> Yes.
> 
> > To make sure that this is root of your problem, can you take some
> > older kernel version (where is i8k working fine) and try to
> > patch+call that i8k_get_fan_type() function? To check that
> > something else cannot interference with it...
> 
> I just tried with 3.19.8 (had to install a older distro first :-/ ),
> where the problem does not show up (I verified just to be sure). Then
> I applied below patch and voila: the fan speed starts going up/down.
> 
> IOW: From what I can see that SMM call that i8k_get_fan_type()
> triggers the problem on my Studio 8000
> 
> CU, knurd
> 

Thank you for your testing! I believe now we definitely know root of 
this problem. It is buggy Dell BIOS/SMM code and we need to avoid 
calling I8K_SMM_GET_FAN_TYPE on affected buggy Dell machines.

-- 
Pali Rohár
pali.rohar@gmail.com

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