linux-kernel - RE: [PATCH 2/2] hwmon: (coretemp) Get TjMax value from MSR

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Date:	Sun, 13 Jun 2010 10:27:17 +0800
From:	"Wan, Huaxu" <huaxu.wan@...el.com>
To:	'Maxim Levitsky' <maximlevitsky@...il.com>,
	'Huaxu Wan' <huaxu.wan@...ux.intel.com>
CC:	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'lm-sensors@...sensors.org'" <lm-sensors@...sensors.org>,
	"'khali@...ux-fr.org'" <khali@...ux-fr.org>
Subject: RE: [PATCH 2/2] hwmon: (coretemp) Get TjMax value from MSR

>On Wed, 2010-06-02 at 23:10 +0300, Maxim Levitsky wrote: 
>> On Wed, 2010-06-02 at 19:34 +0300, Maxim Levitsky wrote: 
>> > On Mon, 2010-05-31 at 09:39 +0800, Huaxu Wan wrote: 
>> > > On 08:39 Sat 29 May, Maxim Levitsky wrote:
>> > > > On Fri, 2010-05-07 at 17:59 +0800, Huaxu Wan wrote: 
>> > > > > The MSR IA32_TEMPERATURE_TARGET contains the TjMax 
>value in the newer
>> > > > > processers.
>> > > > 
>> > > > I know that TjMax on my system is 85, and now coretemp 
>reports wrong
>> > > > temperatures.
>> > > > First of all BIOS using stupid tricks actualy reports 
>CPU temperature
>> > > > through ACPI, and assuming it was correct TjMax is 85.
>> > > > It also shuts down the system if I 'lie' to it that 
>cpu temperature is
>> > > > 85C.
>> > > 
>> > > From the list at [1], the TjMax(Tjunction) of T5450 is 
>100C. Does anyone
>> > > here can make a double check?
>> > > 
>> > > [1] 
>http://ark.intel.com/Product.aspx?id=30787&processor=T5450&spec
>-codes=SLA4F
>> > 
>> > This is very interesting.
>> > 
>> > With TjMax 85C, the CPUs idle temperature is reported at 
>around 45~50C
>> > GPU temperature that is around 50C 
>> > 
>> > BIOS also reports 45~50C.
>> > 
>> > BIOS hooks an SMI to CPU thermal report, and stores the 
>temperature it
>> > read in ram, then ACPI code reads it, reports and passes to the EC
>> > (embedded controller).
>> > 
>> > If I write myself 85 to embedded controller, systems shuts down.
>> > (values less that 85, eg 84 don't shut system).
>> 
>> 
>> Another clue is that right after resume from ram, after long delay
>> (~hour) the displayed temperature with TjMax 85 is 33C. Since room
>> temperature here is around 27C, this seems more plausible that 
>> 33 + 15 = 48C 
>
>
>Any update? 

I'm occupied by other things, sorry for slow response. But, as said in a 
spec, I can't remember which one now, there are too many, the relative
value read from DTS is accurate approaching to TjMax. The accuracy
deteriorates to +-10C at 50C. Any DTS reading below 50C should be
considered to indicate only a temperature below 50C and not a specific
temperature.

So, the value around 50C can't be taken as real chip temperature. I
would like this issue could be confirmed by more users to avoid it as a 
particular case. At the meantime, I still looking for a laptop with T5450, 
this may take some time. 

Thanks
Huaxu --
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