Hi Rafael, thanks for the follow-up!
On Mon, 21 Feb 2022, Rafael J. Wysocki wrote:
Because we promise that user space won't be broken by kernel changes,
it needs to be restored to make wmpower work again.
I'd rather not restore all of it, though, just the part relied on by
wmpower.
Please check if the attached patch (on top of 5.17-rc5) is sufficient to
restore the wmpower functionality.
When I try to build (v5.17-rc5 + patch) with gcc 11.2.0, I get what looks
to be a syntax error in ac.c:
drivers/acpi/ac.c: In function 'acpi_ac_add_fs':
drivers/acpi/ac.c:182:29: error: expected ')' before 'PREFIX'
182 | printk(KERN_WARNING PREFIX "Deprecated procfs I/F for AC is loaded,"
I've attached an error.log; if you'd like I can send along my .config
also.
...
My thoughts about this though -
I did not really expect to get this interface back after I read the commit
message for its removal. I admire your fidelity to the linux user
promise, but I don't want to create trouble for you guys either.
I am happy to put in the legwork to get wmpower working using whatever the
blessed replacement is for the acpi procfs power stuff. Maybe you can
help shed some light on the sysfs interface for me.
I started exploring a bit under /sys/class/power_supply, looking for
replacements for the "present rate" and "last full/remaining capacity"
items under /proc/acpi/battery. Curiously I have two lenovo ThinkPads, a
T510 and a T540p, and one of them has current_now & charge_full/_now, and
the other has power_now & energy_full/_now. Are these the only two
possibilities for rate & capacity? Or are there other potentially others?
I guess the convenient thing about the /proc/acpi/battery interfaces is
that it automatically presents the right info for rate & capacity.
(I felt like I was losing my mind for a bit when I saw the units presented
as "mAh" in one after I was sure I had read "mWh" before... But reading
your patch helped give me a better clue about what was going on there.)
I'm also curious, is the "BAT[0-*]" pattern for battery names consistent,
or are there other possibilities? I had suspected "AC" was the standard
power_supply name for the main AC power, but that turned out not to be the
case on another (HP) laptop that I took a look at. Which leads me to
suspect that "BATX" is not necessarily standard either.
I'm also thinking to enumerate batteries & AC power supplies via
/sys/bus/acpi/drivers/{ac,battery} rather than /sys/class/power_supply, as
surprisingly even a USB-C stick can show up under power_supply, and it's
not obvious if there's a clean way to sort out what's what then.
...
I say all this of course as a laptop end-user, and even with the kernel
source docs in front of me I seem to be feeling my way around in the dark.
I don't know much about the linux acpi internals, and I did not learn
about the acpi procfs power interface being deprecated until after wmpower
stopped working for me this month :)
It seems like part of the difficulty is that there is not much of a
feedback loop for end users to realize that they are using deprecated
procfs interfaces, whether directly in custom battery scripts that scrape
/proc/acpi/battery, or unwittingly through other programs they happen to
use (in this case wmpower). There are no warnings until it's too late.
And even taking a look at what happened the first time it was removed [1],
it seems the conclusion was "some people are still using programs that
rely on the interface, so we'll add it back" ... But it's not obvious if
any effort was made to contact maintainers with a little nudge, to let
them know that it's (still) deprecated and what the replacement interface
is.
Not sure what the general solution is there, but in any case I'll
cheerfully fix up wmpower.
Thanks again and sorry for the long mail :)
Carl
[1] https://lkml.org/lkml/2014/4/21/152
CC [M] drivers/acpi/ac.o
In file included from ./include/linux/kernel.h:29,
from drivers/acpi/ac.c:11:
drivers/acpi/ac.c: In function 'acpi_ac_add_fs':
drivers/acpi/ac.c:182:29: error: expected ')' before 'PREFIX'
182 | printk(KERN_WARNING PREFIX "Deprecated procfs I/F for AC is loaded,"
| ^~~~~~
./include/linux/printk.h:418:25: note: in definition of macro 'printk_index_wra'
418 | _p_func(_fmt, ##__VA_ARGS__); \
| ^~~~
drivers/acpi/ac.c:182:9: note: in expansion of macro 'printk'
182 | printk(KERN_WARNING PREFIX "Deprecated procfs I/F for AC is loaded,"
| ^~~~~~
./include/linux/printk.h:418:24: note: to match this '('
418 | _p_func(_fmt, ##__VA_ARGS__); \
| ^
./include/linux/printk.h:446:26: note: in expansion of macro 'printk_index_wrap'
446 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__)
| ^~~~~~~~~~~~~~~~~
drivers/acpi/ac.c:182:9: note: in expansion of macro 'printk'
182 | printk(KERN_WARNING PREFIX "Deprecated procfs I/F for AC is loaded,"
| ^~~~~~
