Re: Weird Dell SMM bug since 6.18

[Armin Wolf <W_Armin@gmx.de>]

Am 13.03.26 um 20:06 schrieb Jan Claußen:

> I was actually in a fixed state for some reason and everything worked. I then tried to get back to the broken state and seems that echoing 2 into the pwmX_enable endpoints followed by reboot did the trick.

The developers of CoolerControl said that:

	"As mentioned in my previous response above, CC reads the pwmX values first, and if that fails, then it doesn't bother
	 with checking the pwmX_enable attributes. So, according to the logs, it's never getting to the point of reading the
	 pwmX_enable files at all, ..."

Reading pwmX when the associated PWM channel is still in automatic control mode will return -ENODATA because
the driver cannot retrieve the current PWM value when the BIOS controls the fan. This likely causes CoolerControl
to ignore the dell-smm hwmon device.

There a two solutions for this:
1. CoolerControl does not ignore PWM channels that cannot be read when in automatic control mode (or adds some special handling for this driver).
2. The dell-smm-hwmon driver stops returning -ENODATA and instead returns a dummy value (like 0).

Guenter, would you be OK with the second approach? I get the feeling that this issue might affect more
fan control daemons.

Thanks,
Armin Wolf

>
> I then reverted the commits you suggested and it indeed fixed the issue. What to do now? Should coolercontrol adjust its code to this change or the commit be get reverted upstream?
>
> My two cents regarding cranking the fans up to max until the control software kicks in: I think medium fan speed should be sufficent. I actually would always default to BIOS control and make the control software in userspace responsible for setting pwmX_enable.

The problem is that on some devices, the "medium" setting is veeeeeery low, so the device might overheat should the fan control daemon somehow fail
to start. Normally this maximum speed is quickly overwritten by the fan control daemon after entering manual control mode, so this should not be a problem
in this case.

Thanks,
Armin Wolf

> Regards,
> Jan
>