Re: [PATCH] dell-smm-hwmon.c: Additional temperature sensors

From: Michele Sorcinelli <michelesr@autistici.org>
To: "Pali Rohár" <pali.rohar@gmail.com>
Cc: Guenter Roeck <linux@roeck-us.net>, linux-hwmon@vger.kernel.org
Subject: Re: [PATCH] dell-smm-hwmon.c: Additional temperature sensors
Date: Sun, 21 Apr 2019 18:00:37 +0100	[thread overview]
Message-ID: <3222ea02-52fb-78fe-41dc-aa1cf6e5cf4b@autistici.org> (raw)
In-Reply-To: <20190207124010.zfqyn2vzgwkatima@pali>

I think they'll never fix it or release information about the change.
What if we modify the driver to fallback to i8k_get_temp() if i8k_get_temp_type()
fails as a probe method? Or we could add a module option to force that behavior.

Cheers,
Michele.

On 2/7/19 12:40 PM, Pali Rohár wrote:
> Do you have definite response from Dell support that they are not going
> to fix it? Then it is pity :-(
> 
> On Thursday 07 February 2019 12:16:06 Michele Sorcinelli wrote:
>> As far as I know Dell won't help with fixing the SMM layer, they probably
>> changed something starting with firmware version 1.3.0 and they don't
>> wanna release information about it.
>>
>> https://www.hwinfo.com/forum/Thread-Dell-XPS-15-9570-temperatures-not-named-anymore
>>
>> I wonder if something can be done to force the discovery of the sensors in the driver,
>> maybe adding a module option to use i8k_get_temp() as probe method as a workaround,
>> or maybe just forcing that method for this specific model?
>>
>> Let me know your thoughts.
>>
>> Thanks,
>> Michele.
>>
>> On 12/10/18 10:58 AM, Pali Rohár wrote:
>>> On Friday 07 December 2018 20:24:49 Guenter Roeck wrote:
>>>> Anyway, I would like to get some feedback if this can cause regressions
>>>> on systems which don't support that many sensors and maybe report something
>>>> completely different if one tries to read the high-numbered sensors.
>>>> I seem to recall that there was a reason for checking the type and not just
>>>> trying to read sensor values.
>>>
>>> There can be also different problem for sensors which are turned off.
>>> E.g. on notebooks with switchable graphic cards which have included
>>> temperature sensors. When graphic card is turned off, then SMM returns
>>> error when asking for temperature value (for obvious reason). But
>>> temperature type still returns correct value "this is GPU sensors".
>>>
>>> So we cannot replace temp_type check by temp_value check. It introduce
>>> race condition between "starting GPU" and initializing dell-smm hwmon.
>>> Now linux kernel has support for dynamic turning ON/OFF switchable GPU,
>>> so we need to care about these race conditions too.
>>>
> 