Re: [PATCH v2 1/2] hwmon: add ChromeOS EC driver

[Thomas Weißschuh]

On 2024-05-29 10:58:23+0000, Stephen Horvath wrote:
> On 29/5/24 09:29, Guenter Roeck wrote:
> > On 5/28/24 09:15, Thomas Weißschuh wrote:
> > > On 2024-05-28 08:50:49+0000, Guenter Roeck wrote:
> > > > On 5/27/24 17:15, Stephen Horvath wrote:
> > > > > On 28/5/24 05:24, Thomas Weißschuh wrote:
> > > > > > On 2024-05-25 09:13:09+0000, Stephen Horvath wrote:
> > > > > > > Don't forget it can also return `EC_FAN_SPEED_STALLED`.

<snip>

> > > > > > 
> > > > > > Thanks for the hint. I'll need to think about how to
> > > > > > handle this better.
> > > > > > 
> > > > > > > Like Guenter, I also don't like returning `-ENODEV`,
> > > > > > > but I don't have a
> > > > > > > problem with checking for `EC_FAN_SPEED_NOT_PRESENT`
> > > > > > > in case it was removed
> > > > > > > since init or something.
> > > > > > 
> > > > 
> > > > That won't happen. Chromebooks are not servers, where one might
> > > > be able to
> > > > replace a fan tray while the system is running.
> > > 
> > > In one of my testruns this actually happened.
> > > When running on battery, one specific of the CPU sensors sporadically
> > > returned EC_FAN_SPEED_NOT_PRESENT.
> > > 
> > 
> > What Chromebook was that ? I can't see the code path in the EC source
> > that would get me there.
> > 
> 
> I believe Thomas and I both have the Framework 13 AMD, the source code is
> here:
> https://github.com/FrameworkComputer/EmbeddedController/tree/lotus-zephyr

Correct.

> The organisation confuses me a little, but Dustin has previous said on the
> framework forums (https://community.frame.work/t/what-ec-is-used/38574/2):
> 
> "This one is based on the Zephyr port of the ChromeOS EC, and tracks
> mainline more closely. It is in the branch lotus-zephyr.
> All of the model-specific code lives in zephyr/program/lotus.
> The 13"-specific code lives in a few subdirectories off the main tree named
> azalea."

The EC code is at [0]:

$ ectool version
RO version:    azalea_v3.4.113353-ec:b4c1fb,os
RW version:    azalea_v3.4.113353-ec:b4c1fb,os
Firmware copy: RO
Build info:    azalea_v3.4.113353-ec:b4c1fb,os:7b88e1,cmsis:4aa3ff 2024-03-26 07:10:22 lotus@ip-172-26-3-226
Tool version:  0.0.1-isolate May  6 2024 none


>From the build info I gather it should be commit b4c1fb, which is the
current HEAD of the lotus-zephyr branch.
Lotus is the Framework 16 AMD, which is very similar to Azalea, the
Framework 13 AMD, which I tested this against.
Both share the same codebase.

> Also I just unplugged my fan and you are definitely correct, the EC only
> generates EC_FAN_SPEED_NOT_PRESENT for fans it does not have the capability
> to support. Even after a reboot it just returns 0 RPM for an unplugged fan.
> I thought about simulating a stall too, but I was mildly scared I was going
> to break one of the tiny blades.

I get the error when unplugging *the charger*.

To be more precise:

It does not happen always.
It does not happen instantly on unplugging.
It goes away after a few seconds/minutes.
During the issue, one specific sensor reads 0xffff.

> > > > > > Ok.
> > > > > > 
> > > > > > > My approach was to return the speed as `0`, since
> > > > > > > the fan probably isn't
> > > > > > > spinning, but set HWMON_F_FAULT for `EC_FAN_SPEED_NOT_PRESENT` and
> > > > > > > HWMON_F_ALARM for `EC_FAN_SPEED_STALLED`.
> > > > > > > No idea if this is correct though.
> > > > > > 
> > > > > > I'm not a fan of returning a speed of 0 in case of errors.
> > > > > > Rather -EIO which can't be mistaken.
> > > > > > Maybe -EIO for both EC_FAN_SPEED_NOT_PRESENT (which
> > > > > > should never happen)
> > > > > > and also for EC_FAN_SPEED_STALLED.
> > > > > 
> > > > > Yeah, that's pretty reasonable.
> > > > > 
> > > > 
> > > > -EIO is an i/o error. I have trouble reconciling that with
> > > > EC_FAN_SPEED_NOT_PRESENT or EC_FAN_SPEED_STALLED.
> > > > 
> > > > Looking into the EC source code [1], I see:
> > > > 
> > > > EC_FAN_SPEED_NOT_PRESENT means that the fan is not present.
> > > > That should return -ENODEV in the above code, but only for
> > > > the purpose of making the attribute invisible.
> > > > 
> > > > EC_FAN_SPEED_STALLED means exactly that, i.e., that the fan
> > > > is present but not turning. The EC code does not expect that
> > > > to happen and generates a thermal event in case it does.
> > > > Given that, it does make sense to set the fault flag.
> > > > The actual fan speed value should then be reported as 0 or
> > > > possibly -ENODATA. It should _not_ generate any other error
> > > > because that would trip up the "sensors" command for no
> > > > good reason.
> > > 
> > > Ack.
> > > 
> > > Currently I have the following logic (for both fans and temp):
> > > 
> > > if NOT_PRESENT during probing:
> > >    make the attribute invisible.
> > > 
> > > if any error during runtime (including NOT_PRESENT):
> > >    return -ENODATA and a FAULT
> > > 
> > > This should also handle the sporadic NOT_PRESENT failures.
> > > 
> > > What do you think?
> > > 
> > > Is there any other feedback to this revision or should I send the next?
> > > 
> > 
> > No, except I'd really like to know which Chromebook randomly generates
> > a EC_FAN_SPEED_NOT_PRESENT response because that really looks like a bug.
> > Also, can you reproduce the problem with the ectool command ?

Yes, the ectool command reports the same issue at the same time.

The fan affected was always the sensor cpu@4c, which is
compatible = "amd,sb-tsi".

> I have a feeling it was related to the concurrency problems between ACPI and
> the CrOS code that are being fixed in another patch by Ben Walsh, I was also
> seeing some weird behaviour sometimes but I *believe* it was fixed by that.

I don't think it's this issue.
Ben's series at [1], is for MEC ECs which are the older Intel
Frameworks, not the Framework 13 AMD.

[0] https://github.com/FrameworkComputer/EmbeddedController
[1] https://lore.kernel.org/lkml/20240515055631.5775-1-ben@xxxxxxxxxx/