Miguel Ojeda пишет:
On Sun, Oct 4, 2009 at 11:36 PM, Alexey Starikovskiy
<astarikovskiy@xxxxxxx> wrote:
Hi Rafael,
This is not my rule, it was/is the rule of power device class. If you do not
agree to it, please change
appropriate documentation.
Oh, I did not know that. Thank you for pointing it out. I think you
are refering to:
158Q: Suppose, my battery monitoring chip/firmware does not provides capacity
159 in percents, but provides charge_{now,full,empty}. Should I calculate
160 percentage capacity manually, inside the driver, and register CAPACITY
161 attribute? The same question about time_to_empty/time_to_full.
162A: Most likely, no. This class is designed to export properties which are
163 directly measurable by the specific hardware available.
164
165 Inferring not available properties using some heuristics or mathematical
166 model is not subject of work for a battery driver. Such functionality
167 should be factored out, and in fact, apm_power, the driver to serve
168 legacy APM API on top of power supply class, uses a simple heuristic of
169 approximating remaining battery capacity based on its charge, current,
170 voltage and so on. But full-fledged battery model is likely not subject
171 for kernel at all, as it would require floating point calculation to deal
172 with things like differential equations and Kalman filters. This is
173 better be handled by batteryd/libbattery, yet to be written.
We are not calculating anything new just by the pleasure of doing it,
we are correcting a wrong value provided by the hardware.
You are guessing that normal battery can not jump charge value, and on this assumption you
cap charge_now with last full_charge. Immediate problem is that full_charge is not fixed value,
this is why it is separated from design_full_charge.
During battery life full_charge may go down and up, depending on outside temperature, battery discharge (full or partial).
I've seen batteries on some new machines reporting full charge of more than design charge.
Obviously, your patch will fail in some of the above situations.
Currently, reading from the driver is "last resort" to get un-interpreted value, if you have any doubts on it. With
your patch, this is gone, and user space will have to interpret results of kernel interpreter.
Return to the "bug still exists". We are referring to the value, which can not be measured directly with any known device.
Thus, it may be completely sane that battery manufacturer provides you with some charge curve, but knows only two values on it
which he may trust -- point where he can not get any power out of it (complete discharge) and point where he can not put any additional charge into the battery (due to various stop conditions (battery temperature being one)). In such a case manufacturer may choose to adjust charge curve to end up always at design_full_charge point, no matter how much of adjustment this requires.
Do you have the same jump from >100% to 99% on discharge?
Regards,
Alex.
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