[PATCH v4] HID: logitech-hidpp: battery: provide CAPACITY property for newer devices

[Hamza Mahfooz]

For devices that only support the BATTERY_VOLTAGE (0x1001) feature, UPower
requires the additional information provided by this patch, to set them up.

Signed-off-by: Hamza Mahfooz <someguy@xxxxxxxxxxxxxxxxxxx>
---

v2: use ARRAY_SIZE() and set voltages[]'s size to 100

v3: add a check to ensure that exactly 100 elements are in voltages[]

v4: add a note regarding the voltage curve and introduce a bounds check on
    the reported voltage
---
 drivers/hid/hid-logitech-hidpp.c | 44 +++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
index 61635e629469..c4226883904b 100644
--- a/drivers/hid/hid-logitech-hidpp.c
+++ b/drivers/hid/hid-logitech-hidpp.c
@@ -1331,6 +1331,43 @@ static int hidpp20_battery_get_battery_voltage(struct hidpp_device *hidpp,
 	return 0;
 }
 
+static int hidpp20_map_battery_capacity(struct hid_device *hid_dev, int voltage)
+{
+	/* NB: This voltage curve doesn't necessarily map perfectly to all
+	 * devices that implement the BATTERY_VOLTAGE feature. This is because
+	 * there are a few devices that use different battery technology.
+	 */
+
+	static const int voltages[] = {
+		4186, 4156, 4143, 4133, 4122, 4113, 4103, 4094, 4086, 4075,
+		4067, 4059, 4051, 4043, 4035, 4027, 4019, 4011, 4003, 3997,
+		3989, 3983, 3976, 3969, 3961, 3955, 3949, 3942, 3935, 3929,
+		3922, 3916, 3909, 3902, 3896, 3890, 3883, 3877, 3870, 3865,
+		3859, 3853, 3848, 3842, 3837, 3833, 3828, 3824, 3819, 3815,
+		3811, 3808, 3804, 3800, 3797, 3793, 3790, 3787, 3784, 3781,
+		3778, 3775, 3772, 3770, 3767, 3764, 3762, 3759, 3757, 3754,
+		3751, 3748, 3744, 3741, 3737, 3734, 3730, 3726, 3724, 3720,
+		3717, 3714, 3710, 3706, 3702, 3697, 3693, 3688, 3683, 3677,
+		3671, 3666, 3662, 3658, 3654, 3646, 3633, 3612, 3579, 3537
+	};
+
+	int i;
+
+	BUILD_BUG_ON(ARRAY_SIZE(voltages) != 100);
+
+	if (unlikely(voltage < 3500 || voltage >= 5000))
+		hid_warn_once(hid_dev,
+			      "%s: possibly using the wrong voltage curve\n",
+			      __func__);
+
+	for (i = 0; i < ARRAY_SIZE(voltages); i++) {
+		if (voltage >= voltages[i])
+			return ARRAY_SIZE(voltages) - i;
+	}
+
+	return 0;
+}
+
 static int hidpp20_query_battery_voltage_info(struct hidpp_device *hidpp)
 {
 	u8 feature_type;
@@ -1354,6 +1391,8 @@ static int hidpp20_query_battery_voltage_info(struct hidpp_device *hidpp)
 
 	hidpp->battery.status = status;
 	hidpp->battery.voltage = voltage;
+	hidpp->battery.capacity = hidpp20_map_battery_capacity(hidpp->hid_dev,
+							       voltage);
 	hidpp->battery.level = level;
 	hidpp->battery.charge_type = charge_type;
 	hidpp->battery.online = status != POWER_SUPPLY_STATUS_NOT_CHARGING;
@@ -1378,6 +1417,8 @@ static int hidpp20_battery_voltage_event(struct hidpp_device *hidpp,
 
 	if (voltage != hidpp->battery.voltage || status != hidpp->battery.status) {
 		hidpp->battery.voltage = voltage;
+		hidpp->battery.capacity = hidpp20_map_battery_capacity(hidpp->hid_dev,
+								       voltage);
 		hidpp->battery.status = status;
 		hidpp->battery.level = level;
 		hidpp->battery.charge_type = charge_type;
@@ -3717,7 +3758,8 @@ static int hidpp_initialize_battery(struct hidpp_device *hidpp)
 	num_battery_props = ARRAY_SIZE(hidpp_battery_props) - 3;
 
 	if (hidpp->capabilities & HIDPP_CAPABILITY_BATTERY_MILEAGE ||
-	    hidpp->capabilities & HIDPP_CAPABILITY_BATTERY_PERCENTAGE)
+	    hidpp->capabilities & HIDPP_CAPABILITY_BATTERY_PERCENTAGE ||
+	    hidpp->capabilities & HIDPP_CAPABILITY_BATTERY_VOLTAGE)
 		battery_props[num_battery_props++] =
 				POWER_SUPPLY_PROP_CAPACITY;
 
-- 
2.32.0