v4.10-rc4 to v4.10-rc5: battery regression on Nokia N900

On Thu, 2017-01-26 at 22:27 -0800, Guenter Roeck wrote:

On 01/26/2017 07:39 PM, Zhang Rui wrote:

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On Thu, 2017-01-26 at 18:03 -0800, Guenter Roeck wrote:

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On 01/26/2017 05:37 PM, Zhang Rui wrote:

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On Wed, 2017-01-25 at 13:09 +0100, Pali Roh?r wrote:

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On Wednesday 25 January 2017 12:12:33 Pavel Machek wrote:

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Hi!

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Right.

Before reverting, can you please try if this
patch
works
or not?

Not really. Revert now. Sorry.

Are you sure? This does not look equivalent to me
at
all.

"name" file handling moved from drivers to the
core,
which
added some
crazy checks what name can contain. Even if this
"works",
what is the
expected effect on the "name" file?

The hwmon name attribute must not include '-', as
documented
in
Documentation/hwmon/sysfs-interface. Is enforcing
that
'crazy' ?
Maybe in your world, but not in mine.

Well, lets revert the patch and then we can discuss
what to
do
with
the "name" problem.

Ok, so the patch is on the way in. What to do next?

pavel at n900:/sys/class/hwmon$ cat hwmon0/name
bq27200-0
pavel at n900:/sys/class/hwmon$ cat hwmon1/name
rx51-battery

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To provide some detail: libsensors gets just as confused
with
wildcards
and whitespace/newline as it does with '-' in the
reported
name,
which
is why those are blocked by the new API.

Ok... Question is "does someone actually use hwmon*/name on
N900"?
If
so, we can't change it, but it is well possible that noone
is.

IIRC hwmon is used on Nokia N900.

But I have not seen hwmon devices for bq27200 and rx51-
battery
yet.
Those are power supply driver and auto-exporting them also
via
hwmon
is
something new, right? If yes, then we can use any name for
those
new
hwmon devices as they cannot break userspace... as there is
no
userspace
application for them.

If this is the case, you'd better set
(struct thermal_zone_params)->no_hwmon when registering the
thermal
zone device, in which case, the hwmon device will not be
created.

In fact, I'd prefer to change tzp->no_hwmon to tzp->hwmon to
not
create
hwmon I/F by default, and see if there is anyone using it. If
yes,
we
can set the flag in soc thermal driver, explicitly, at
meantime, a
hwmon compatible name is required.

But one foreseeable result is that we may get bug reports from
end
user
that some sensors (acpitz, etc) are gone in 'sensors' output.
And
TBH,
I'm not quite sure if this can be counted as a regression or
not.

That sounds like fun. Changing bq27200-0 to bq27200_0 is
Forbidden by
the ABI Police, but taking the entire device away is ok.

No. IMO, it depends on if the interface is used or not.
If hwmon I/F is used, we can not take it away, nor change its name.

Even if the use doesn't depend on that name ?

when I said "the interface is used", I mean the name string is used.

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If thermal zone I/F is used, we can not change it's 'type' name to
be
compatible with new hwmon API.

You mean you can not fix the name to be compatible with libsensors.

We can try to convert it to a libsensor-compatible string, either for
hwmon only, or for both thermal and hwmon. But this is an ABI change,
right?
And my understanding about the ABI change is that, if no one cares
about it, we're okay, or else, this is a regression, and we need to
fall back to the previous ABI immediately. In order to change it in a
long run, we need to make a note in Documentation/ABI/, and change it
sometime in the future (a couple of release cycles or even more).
This also happens when I was trying to delete the obsoltete

thanks,
rui

Makes me wonder if there shouldn't be a rule that exploits must not
be fixed if already exploited.

Guenter

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Anyway, sounds good to me. No one will use something that isn't
there,
and no one will realize that it could have been there, so I don't
expect
anyone to complain.

Yes, I agree.

thanks,
rui