ACPI / battery: Correct battery capacity values on Thinkpads

Add a quirk to correctly report battery capacity on 2010 and 2011
Lenovo Thinkpad models.

The affected models that I tested (x201, t410, t410s, and x220)
exhibit a problem where, when battery capacity reporting unit is mAh,
the values being reported are wrong.  Pre-2010 and 2012 models appear
to always report in mWh and are thus unaffected.  Also, in mid-2012
Lenovo issued a BIOS update for the 2011 models that fixes the issue
(tested on x220 with a post-1.29 BIOS).  No such update is available
for the 2010 models, so those still need this patch.

Problem description: for some reason, the affected Thinkpads switch
the reporting unit between mAh and mWh; generally, mAh is used when a
laptop is plugged in and mWh when it's unplugged, although a
suspend/resume or rmmod/modprobe is needed for the switch to take
effect.  The values reported in mAh are *always* wrong.  This does
not appear to be a kernel regression; I believe that the values were
never reported correctly.  I tested back to kernel 2.6.34, with
multiple machines and BIOS versions.

Simply plugging a laptop into mains before turning it on is enough to
reproduce the problem.  Here's a sample /proc/acpi/battery/BAT0/info
from Thinkpad x220 (before a BIOS update) with a 4-cell battery:

present:                 yes
design capacity:         2886 mAh
last full capacity:      2909 mAh
battery technology:      rechargeable
design voltage:          14800 mV
design capacity warning: 145 mAh
design capacity low:     13 mAh
cycle count:              0
capacity granularity 1:  1 mAh
capacity granularity 2:  1 mAh
model number:            42T4899
serial number:           21064
battery type:            LION
OEM info:                SANYO

Once the laptop switches the unit to mWh (unplug from mains, suspend,
resume), the output changes to:

present:                 yes
design capacity:         28860 mWh
last full capacity:      29090 mWh
battery technology:      rechargeable
design voltage:          14800 mV
design capacity warning: 1454 mWh
design capacity low:     200 mWh
cycle count:              0
capacity granularity 1:  1 mWh
capacity granularity 2:  1 mWh
model number:            42T4899
serial number:           21064
battery type:            LION
OEM info:                SANYO

Can you see how the values for "design capacity", etc., differ by a
factor of 10 instead of 14.8 (the design voltage of this battery)?
On the battery itself it says: 14.8V, 1.95Ah, 29Wh, so clearly the
values reported in mWh are correct and the ones in mAh are not.

My guess is that this problem has been around ever since those
machines were released, but because the most common Thinkpad
batteries are rated at 10.8V, the error (8%) is small enough that it
simply hasn't been noticed or at least nobody could be bothered to
look into it.

My patch works around the problem by adjusting the incorrectly
reported mAh values by "10000 / design_voltage".  The patch also has
code to figure out if it should be activated or not.  It only
activates on Lenovo Thinkpads, only when the unit is mAh, and, as an
extra precaution, only when the battery capacity reported through
ACPI does not match what is reported through DMI (I've never
encountered a machine where the first two conditions would be true
but the last would not, but better safe than sorry).

I've been using this patch for close to a year on several systems
without any problems.

References: https://bugzilla.kernel.org/show_bug.cgi?id=41062
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/battery.c

@@ -34,6 +34,7 @@
 #include <linux/dmi.h>
 #include <linux/slab.h>
 #include <linux/suspend.h>
+#include <asm/unaligned.h>
 
 #ifdef CONFIG_ACPI_PROCFS_POWER
 #include <linux/proc_fs.h>
@@ -95,6 +96,18 @@ enum {
 	ACPI_BATTERY_ALARM_PRESENT,
 	ACPI_BATTERY_XINFO_PRESENT,
 	ACPI_BATTERY_QUIRK_PERCENTAGE_CAPACITY,
+	/* On Lenovo Thinkpad models from 2010 and 2011, the power unit
+	   switches between mWh and mAh depending on whether the system
+	   is running on battery or not.  When mAh is the unit, most
+	   reported values are incorrect and need to be adjusted by
+	   10000/design_voltage.  Verified on x201, t410, t410s, and x220.
+	   Pre-2010 and 2012 models appear to always report in mWh and
+	   are thus unaffected (tested with t42, t61, t500, x200, x300,
+	   and x230).  Also, in mid-2012 Lenovo issued a BIOS update for
+	   the 2011 models that fixes the issue (tested on x220 with a
+	   post-1.29 BIOS), but as of Nov. 2012, no such update is
+	   available for the 2010 models.  */
+	ACPI_BATTERY_QUIRK_THINKPAD_MAH,
 };
 
 struct acpi_battery {
@@ -438,6 +451,21 @@ static int acpi_battery_get_info(struct acpi_battery *battery)
 	kfree(buffer.pointer);
 	if (test_bit(ACPI_BATTERY_QUIRK_PERCENTAGE_CAPACITY, &battery->flags))
 		battery->full_charge_capacity = battery->design_capacity;
+	if (test_bit(ACPI_BATTERY_QUIRK_THINKPAD_MAH, &battery->flags) &&
+	    battery->power_unit && battery->design_voltage) {
+		battery->design_capacity = battery->design_capacity *
+		    10000 / battery->design_voltage;
+		battery->full_charge_capacity = battery->full_charge_capacity *
+		    10000 / battery->design_voltage;
+		battery->design_capacity_warning =
+		    battery->design_capacity_warning *
+		    10000 / battery->design_voltage;
+		/* Curiously, design_capacity_low, unlike the rest of them,
+		   is correct.  */
+		/* capacity_granularity_* equal 1 on the systems tested, so
+		   it's impossible to tell if they would need an adjustment
+		   or not if their values were higher.  */
+	}
 	return result;
 }
 
@@ -486,6 +514,11 @@ static int acpi_battery_get_state(struct acpi_battery *battery)
 	    && battery->capacity_now >= 0 && battery->capacity_now <= 100)
 		battery->capacity_now = (battery->capacity_now *
 				battery->full_charge_capacity) / 100;
+	if (test_bit(ACPI_BATTERY_QUIRK_THINKPAD_MAH, &battery->flags) &&
+	    battery->power_unit && battery->design_voltage) {
+		battery->capacity_now = battery->capacity_now *
+		    10000 / battery->design_voltage;
+	}
 	return result;
 }
 
@@ -595,6 +628,24 @@ static void sysfs_remove_battery(struct acpi_battery *battery)
 	mutex_unlock(&battery->sysfs_lock);
 }
 
+static void find_battery(const struct dmi_header *dm, void *private)
+{
+	struct acpi_battery *battery = (struct acpi_battery *)private;
+	/* Note: the hardcoded offsets below have been extracted from
+	   the source code of dmidecode.  */
+	if (dm->type == DMI_ENTRY_PORTABLE_BATTERY && dm->length >= 8) {
+		const u8 *dmi_data = (const u8 *)(dm + 1);
+		int dmi_capacity = get_unaligned((const u16 *)(dmi_data + 6));
+		if (dm->length >= 18)
+			dmi_capacity *= dmi_data[17];
+		if (battery->design_capacity * battery->design_voltage / 1000
+		    != dmi_capacity &&
+		    battery->design_capacity * 10 == dmi_capacity)
+			set_bit(ACPI_BATTERY_QUIRK_THINKPAD_MAH,
+				&battery->flags);
+	}
+}
+
 /*
  * According to the ACPI spec, some kinds of primary batteries can
  * report percentage battery remaining capacity directly to OS.
@@ -620,6 +671,32 @@ static void acpi_battery_quirks(struct acpi_battery *battery)
 		battery->capacity_now = (battery->capacity_now *
 				battery->full_charge_capacity) / 100;
 	}
+
+	if (test_bit(ACPI_BATTERY_QUIRK_THINKPAD_MAH, &battery->flags))
+		return ;
+
+	if (battery->power_unit && dmi_name_in_vendors("LENOVO")) {
+		const char *s;
+		s = dmi_get_system_info(DMI_PRODUCT_VERSION);
+		if (s && !strnicmp(s, "ThinkPad", 8)) {
+			dmi_walk(find_battery, battery);
+			if (test_bit(ACPI_BATTERY_QUIRK_THINKPAD_MAH,
+				     &battery->flags) &&
+			    battery->design_voltage) {
+				battery->design_capacity =
+				    battery->design_capacity *
+				    10000 / battery->design_voltage;
+				battery->full_charge_capacity =
+				    battery->full_charge_capacity *
+				    10000 / battery->design_voltage;
+				battery->design_capacity_warning =
+				    battery->design_capacity_warning *
+				    10000 / battery->design_voltage;
+				battery->capacity_now = battery->capacity_now *
+				    10000 / battery->design_voltage;
+			}
+		}
+	}
 }
 
 static int acpi_battery_update(struct acpi_battery *battery)