Date: Sat, 06 Dec 2014 23:53:37 -0800 From: Colin Percival <cperciva@freebsd.org> To: freebsd-acpi@freebsd.org Subject: ENXIOing non-present battery Message-ID: <54840781.70603@freebsd.org>
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Hi ACPI people,
On my Dell Latitude E7440 laptop, the ACPI reports two batteries: First
the battery which exists; and second, a "Not Present" battery with zeroed
statistics. FreeBSD, not realizing that this second battery is a complete
myth -- the E7440 only has one battery, and there is nowhere to add another
-- faithfully reports the data from ACPI to userland.
Unfortunately it causes some problems there; in particular, KDE interprets
it as meaning that the system should have two batteries, and when it sees
that the "second" battery has 0% power remaining it kicks off the "battery
is low, turn the laptop off" code. If that code is disabled, it still
displays the wrong battery-charge-remaining status icons.
For dealing with such broken ACPIs, it seems like not attaching a non-present
battery would be a good idea. This shouldn't be the default behaviour, since
there are plenty of systems where a non-present battery might be inserted at
a later time; but I see nothing wrong with adding an option.
The attached patch adds a acpi.cmbat.hide_not_present loader tunable which,
as the name suggests, hides non-present batteries; this is done in the probe
code by returning ENXIO if the tunable is set to a nonzero value and
acpi_BatteryIsPresent returns zero. With this patch and the tunable set my
laptop behaves appropriately; and (aside from wasting a few bytes of memory)
there should be no effect on systems where the tunable is not set.
Any objections to me committing this?
--
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid
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Index: sys/dev/acpica/acpi_cmbat.c
===================================================================
--- sys/dev/acpica/acpi_cmbat.c (revision 274932)
+++ sys/dev/acpica/acpi_cmbat.c (working copy)
@@ -112,13 +112,17 @@
DRIVER_MODULE(acpi_cmbat, acpi, acpi_cmbat_driver, acpi_cmbat_devclass, 0, 0);
MODULE_DEPEND(acpi_cmbat, acpi, 1, 1, 1);
+static unsigned long hide_not_present = 0;
+TUNABLE_ULONG("acpi.cmbat.hide_not_present", &hide_not_present);
+
static int
acpi_cmbat_probe(device_t dev)
{
static char *cmbat_ids[] = { "PNP0C0A", NULL };
if (acpi_disabled("cmbat") ||
- ACPI_ID_PROBE(device_get_parent(dev), dev, cmbat_ids) == NULL)
+ ACPI_ID_PROBE(device_get_parent(dev), dev, cmbat_ids) == NULL ||
+ (hide_not_present && !acpi_BatteryIsPresent(dev)))
return (ENXIO);
device_set_desc(dev, "ACPI Control Method Battery");
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