Messages in this thread | | | Subject | Re: [PATCH 5/5] power: supply: bq27xxx: Correct supply status with current draw | From | Paul Kocialkowski <> | Date | Thu, 08 Jun 2017 13:08:52 +0300 |
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Hey,
On Wed, 2017-06-07 at 21:50 +0200, Pavel Machek wrote: > Hi! > > > On Wed, 2017-06-07 at 09:52 +0200, Pavel Machek wrote: > > > > [0]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/ > > > > comm > > > > it/? > > > > h=v4.12-rc4&id=7f93e1fa032bb5ee19b868b9649bc98c82553003 > > > > > > Is there some documentation that explains what different power supply > > > statuses mean? Because without that, we can have long and useless > > > discussions. > > > > Well, I couldn't really find much except the following from Documentation/ > > (which is not that helpful, and the BATTERY_STATUS_* don't seem to exist > > anymore): > > > > " STATUS - this attribute represents operating status (charging, full, > > discharging (i.e. powering a load), etc.). This corresponds to > > BATTERY_STATUS_* values, as defined in battery.h. " > > > > Generally speaking, I think the question to be asked is what information > > users > > will be interested in in each scenario we have to consider. > > Hmm. We really should add some documentation :-(.
Maybe we should start a new thread about this to give it more visibility. That way, PM maintainers could weigh-in and share thoughts.
I definitely agree there is a need to clarify what we want to report to userspace given the various scenarios we've been discussing.
> > > If you have 40Wh battery, and you are charging it with 1mW, I don't > > > believe you should be indicating "charging". That battery is > > > full. Yes, even full batteries are sometimes charged with very low > > > currents to keep them full. > > > > That makes sense. Note that this patch was however designed to solve the > > problem > > the other way round: my device will report full battery when the PSU was > > disconnected and that it is, in fact, drawing significant current. > > That is documented / correct behaviour sometimes. Thinkpad batteries > have thresholds -- lets say 100% and 95%. They charge battery to full > (as expected), but then they won't start charging battery again unless > it drops below 95%. So you can have "battery full, charger > disconnected" state. > > [Design like this prolongs longevity of li-ion batteries.]
That is definitely good to know.
> > > And I'm not sure what this is supposed to do, but its quite strange > > > code. > > > > Could you comment on what is strange about it? This function corrects the > > status > > based on the current flow as explained through this thread. > > > > > +static int sbs_status_correct(struct i2c_client *client, int *intval) > > > +{ > > > + int ret; > > > + > > > + ret = sbs_read_word_data(client, sbs_data[REG_CURRENT].addr); > > > + if (ret < 0) > > > + return ret; > > > + > > > + ret = (s16)ret; > > The last line ... is strange.
The trick here is that sbs_read_word_data will return a negative value (on 32 bits) when an error (say, I/O related) happens, but the current (returned directly by the call) can also have a legit negative value (current draw).
However, the current value is stored on 16 bytes, so the trick is the use the upper 2 remaining bytes for error reporting and if there's no error, cast the value to a signed 16-bit value to get the (legit) signed current value.
-- Paul Kocialkowski, developer of free digital technology and hardware support
Website: https://www.paulk.fr/ Coding blog: https://code.paulk.fr/ Git repositories: https://git.paulk.fr/ https://git.code.paulk.fr/
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