Re: [PATCH RESEND] iwlwifi, Do not implement thermal zone unless ucode is loaded

On 07/11/2016 02:27 PM, Grumbach, Emmanuel wrote:

On Mon, 2016-07-11 at 14:19 -0400, Prarit Bhargava wrote:

quoted

On 07/11/2016 02:00 PM, Emmanuel Grumbach wrote:

quoted

On Mon, Jul 11, 2016 at 6:18 PM, Prarit Bhargava <prarit@redhat.com

quoted

wrote:

Didn't get any feedback or review comments on this patch. 
 Resending ...

P.

This change is obviously completely broken. It simply disables the
registration to thermal zone core.

No it is not broken, and yes, that is exactly what should happen IMO.

The problem is that the iwlwifi driver implements the thermal zone
even when the
device doesn't support it.

We implement thermal zone because we do support it, but the problem is
that we need the firmware to be loaded for that. So you can argue that
we should register *later* when the firmware is loaded. But this is
really not helping all that much because the firmware can also be
stopped at any time. So you'd want us to register / unregister the
thermal zone anytime the firmware is loaded / unloaded?

You might have to do that.  I think that if the firmware enables a feature then
the act of loading the firmware should run the code that enables the feature.
IMO of course.

I guess that works, but it seems wrong to me. Usually, registration
should happen only upon INIT, and yes, at that time the firmware is not
ready to provide the information yet.
Maybe returning -EBUSY would help lm-sensors not to get confused?

I'll give that a shot, but I expect that won't work either as an error message
will still be displayed.

quoted

As can be seen in the current code base, iwl_mvm_tzone_get_temp()
will return
-EIO 100% of the time when the firmware doesn't support reading the
temperature[1].  In this case a read of sysfs will result in a return
of -EIO,
and this breaks existing userspace programs such as lm-sensors (which
by all
accounts is bad to do).

Right, but I don't understand why the userspace is broken because of
that? 

Before the iwlwifi change, sensors successfully returned.  Now, because of the
error, it doesn't.

Unless we register / unregister anytime the firmware is loaded, I

don't see any proper way to fix this. And yes, I'd expect the userspace
to handle gracefully failures in its requests.

I agree with you in principle *and there's a great many things I wish userspace
would do gracefully* but updating the kernel shouldn't result in userspace
programs failing.

quoted

Note that in my patch I have removed the -EIO return in favor of not
registering
the non-existent thermal zone.  I'm not removing any functionality by
changing
this, nor am I adding functionality.  In both cases the thermal zone
is not
functional, and with my patch userspace continues to work.

You are removing the thermal zone functionality since even when the
firmware will be loaded (which typically happens fairly quickly),
thermal zone won't work.

Then I agree with your suggestion above that you need to enable the thermal zone
on a successful load of the firmware.  [Aside: I wonder what other drivers do in
this situation?  While this does seem like an odd case, I can't believe that the
iwlwifi driver is the only driver to enable features based on firmware.]

P.