Re: [PATCH] i8k: Ignore temperature sensors which report invalid values

From: Guenter Roeck
Date: Tue Nov 18 2014 - 00:56:20 EST

On 11/17/2014 12:35 AM, Pali RohÃr wrote:
On Thursday 23 October 2014 18:45:07 Guenter Roeck wrote:
On Thu, Oct 23, 2014 at 12:37:34PM +0200, Pali RohÃr wrote:
On Wednesday 22 October 2014 19:10:05 Guenter Roeck wrote:
On Wed, Oct 22, 2014 at 06:35:53PM +0200, Pali RohÃr wrote:
On Wednesday 22 October 2014 18:19:47 Guenter Roeck
On Wed, Oct 22, 2014 at 02:29:06PM +0200, Pali RohÃr
On Tuesday 21 October 2014 06:27:23 Guenter Roeck
On 10/20/2014 09:46 AM, Pali RohÃr wrote:
Ok, I will describe my problem. Guenter, maybe
you can find another solution/fix for it.

Calling i8k_get_temp(3) on my laptop without
I8K_TEMPERATURE_BUG always returns value 193
(which is above I8K_MAX_TEMP).

When I8K_TEMPERATURE_BUG is enabled (by default)
then i8k_get_temp(3) returns value from prev[3]
and store new value I8K_TEMPERATURE_BUG to
prev[3]. Value in prev[3] is initialized to 0.

What I want to achieve is: when i8k_get_temp()
for particular sensor id always returns invalid
value (> I8K_MAX_TEMP) then we should totally
ignore sensor with that id and do not export it
via hwmon.

My solution is: initialize prev[id] to
I8K_MAX_TEMP, so on invalid data first call to
i8k_get_temp(id) returns I8K_MAX_TEMP. Then in
i8k_init_hwmon check if value is < I8K_MAX_TEMP
and if not ignore sensor id.

Guenter, it is clear now? Are you ok that we
should ignore sensor if always report value
above I8K_MAX_TEMP? If you do not like my
solution/patch for it, can you specify how
other can it be fixed?

I still don't see the point in initializing

Now prev[] is initialized to 0. It means that first
call i8k_get_temp() (with sensor id which return
value > I8K_MAX_TEMP) returns 0. Second and other
calls returns I8K_MAX_TEMP.

So point is to return same value for first and other

Yes, I realized that after I sent my previous mail.

Yes, I am ok with ignoring sensor values if the
reported temperature is above I8K_MAX_TEMP. I am
just not sure if we should check against
I8K_MAX_TEMP or against, say, 192. Reason is that
we do know that the sensor can erroneously return
0x99 on some systems once in a while. We would
not want to ignore those sensors just because
they happen to report 0x99 during initialization.

So maybe make it

if (err >= 0 && err < 192)

and add a note before the first if(), explaining
that higher values suggest that there is no
sensor attached.


Right, now we need to decide which magic constant to

And now I found another problem :-)

On my laptop i8k_get_temp(3) not always return value
193. It is only when AMD graphics card is turned
off. When card is on i8k_get_temp(3) returns same
value as temperature hwmon part from radeon DRM

Can you turn the GPU on or off during runtime ?
That would make it really tricky to handle the

Yes. New laptops with Nvidia Optimus or AMD PowerXpress
or Enduro technology are designed to automatically turn
off secondary GPU when is not in use. And
nouveau/radeon drivers together with vga_switcheroo
implements this dynamic power on/off.

So it looks like that on my laptop i8k sensor with
id 3 reports GPU temperature.

When card is turned off radeon driver reports
-EINVAL for temperature hwmon sysnode.

So now I think i8k could not ignore sensor totally
as it can be mapped to some HW which can be
dynamically turned on/off (like my graphics card).

So what do you think about reporting -EINVAL instead
I8K_MAX_TEMP when dell SMM returns value above

-EINVAL is supposed to mean "Invalid Argument", so it
really has ia different semantics. We could use
-ENXIO, "No such device or address", which seems more

I prefer to use -EINVAL because other driver (radeon) is
using it and userspace "sensors" programs handle EINVAL
and show "N/A" in output instead reporting some error
about reading value. If nothing else consistency (with
other drivers) is my argument.

Ok, if sensors implements it that way then let's do it.

Overall, I think the entire error handling is broken
and should be replaced. One option would be to
explicitly check for 0x99 and, if detected, go to
sleep for, say, 100ms and try again. If it still
fails, and for all other bad values, return -ENXIO.
Then the calling code can either return the error to
user space in the show function, or not install the
sensor in the probe function.

Does that make sense ?

Yes, replacing error handling with retry call (after
some sleep) is better then current code (which returns
previous value or returns I8K_MAX_TEMP).

But your solution not install the sensor if probe fails
on bad value does not solve problem that i8k.ko is
loading at time when GPU card is turned off.

Yes, the dynamics in that situation makes it a bit
difficult to handle the situation.

I think current check for installing sensor (err < 0) is
enough and when invalid value (> I8K_MAX_TEMP) is
returned just do not show this value for userspace in
hwmon sysnode.

Ok with me, and agreed.


Ok, are you going to fix i8k_get_temp() function (with

I had hoped you would find the time to do it ;-).

Sure, I can do it, but I am kind of busy right now, so it will
take a while.


Ok. Will you do that for 3.19 kernel? Meanwhile I can prepare
patch for temperature labels. I looked into NBSVC.MDM and there
is something related for type of temperature sensors...

Highly unlikely. I don't have the time right now.


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