[RFC PATCH v3 2/9] power: supply: add cap2ocv batinfo helper

[Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>]

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The power-supply core supports concept of OCV (Open Circuit Voltage) =>
SOC (State Of Charge) conversion tables. Usually these tables are used
to estimate SOC based on OCV. Some systems use so called "Zero Adjust"
where at the near end-of-battery condition the SOC from coulomb counter
is used to retrieve the OCV - and OCV and VSYS difference is used to
re-estimate the battery capacity.

Add helper to do look-up the other-way around and also get the OCV
based on SOC

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>

---
RFC v3:
 - Kerneldoc fixes
---
 drivers/power/supply/power_supply_core.c | 69 ++++++++++++++++++++++++
 include/linux/power_supply.h             |  5 ++
 2 files changed, 74 insertions(+)

diff --git a/drivers/power/supply/power_supply_core.c b/drivers/power/supply/power_supply_core.c
index fc12a4f407f4..295672165836 100644
--- a/drivers/power/supply/power_supply_core.c
+++ b/drivers/power/supply/power_supply_core.c
@@ -806,6 +806,48 @@ int power_supply_temp2resist_simple(struct power_supply_resistance_temp_table *t
 }
 EXPORT_SYMBOL_GPL(power_supply_temp2resist_simple);
 
+/**
+ * power_supply_dcap2ocv_simple() - find the battery OCV by capacity
+ * @table: Pointer to battery OCV/CAP lookup table
+ * @table_len: OCV/CAP table length
+ * @cap: Current cap value in units of 0.1%
+ *
+ * OCV (Open Circuit Voltage) is often used to estimate the battery SOC (State
+ * Of Charge). Usually conversion tables are used to store the corresponding
+ * OCV and SOC. Systems which use so called "Zero Adjust" where at the near
+ * end-of-battery condition the SOC from coulomb counter is used to retrieve
+ * the OCV - and OCV and VSYS difference is used to re-estimate the battery
+ * capacity. This helper function can be used to look up battery OCV according
+ * to current capacity value from one OCV table, and the OCV table must be
+ * ordered descending.
+ *
+ * Return: the battery OCV in uV.
+ */
+int power_supply_dcap2ocv_simple(struct power_supply_battery_ocv_table *table,
+				int table_len, int dcap)
+{
+	int i, ocv, tmp;
+
+	for (i = 0; i < table_len; i++)
+		if (dcap > table[i].capacity * 10)
+			break;
+
+	if (i > 0 && i < table_len) {
+		tmp = (table[i - 1].ocv - table[i].ocv) *
+		      (dcap - table[i].capacity * 10);
+
+		tmp /= (table[i - 1].capacity - table[i].capacity) * 10;
+		ocv = tmp + table[i].ocv;
+	} else if (i == 0) {
+		ocv = table[0].ocv;
+	} else {
+		ocv = table[table_len - 1].ocv;
+	}
+
+	return ocv;
+}
+EXPORT_SYMBOL_GPL(power_supply_dcap2ocv_simple);
+
 /**
  * power_supply_ocv2cap_simple() - find the battery capacity
  * @table: Pointer to battery OCV lookup table
@@ -866,6 +908,33 @@ power_supply_find_ocv2cap_table(struct power_supply_battery_info *info,
 }
 EXPORT_SYMBOL_GPL(power_supply_find_ocv2cap_table);
 
+/**
+ * power_supply_batinfo_dcap2ocv() - Compute OCV based on SOC
+ * @info: Pointer to battery information.
+ * @dcao: Battery capacity in units of 0.1%
+ * @temp: Temperatur in Celsius
+ *
+ * Compute the open circuit voltage at given temperature matching given
+ * capacity for a battery described by given battery info. Computation is
+ * done based on tables of known capacity - open circuit voltage value pairs.
+ * Requires the OCV tables being populated in the battery info.
+ *
+ * Return: The battery OCV in uV or -EINVAL if OCV table is not available.
+ */
+int power_supply_batinfo_dcap2ocv(struct power_supply_battery_info *info,
+				 int dcap, int temp)
+{
+	struct power_supply_battery_ocv_table *table;
+	int table_len;
+
+	table = power_supply_find_ocv2cap_table(info, temp, &table_len);
+	if (!table)
+		return -EINVAL;
+
+	return power_supply_dcap2ocv_simple(table, table_len, dcap);
+}
+EXPORT_SYMBOL_GPL(power_supply_batinfo_dcap2ocv);
+
 int power_supply_batinfo_ocv2cap(struct power_supply_battery_info *info,
 				 int ocv, int temp)
 {
diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
index 9ca1f120a211..fa8cf434f7e3 100644
--- a/include/linux/power_supply.h
+++ b/include/linux/power_supply.h
@@ -410,11 +410,16 @@ extern void power_supply_put_battery_info(struct power_supply *psy,
 					  struct power_supply_battery_info *info);
 extern int power_supply_ocv2cap_simple(struct power_supply_battery_ocv_table *table,
 				       int table_len, int ocv);
+int power_supply_dcap2ocv_simple(struct power_supply_battery_ocv_table *table,
+				int table_len, int dcap);
+
 extern struct power_supply_battery_ocv_table *
 power_supply_find_ocv2cap_table(struct power_supply_battery_info *info,
 				int temp, int *table_len);
 extern int power_supply_batinfo_ocv2cap(struct power_supply_battery_info *info,
 					int ocv, int temp);
+int power_supply_batinfo_dcap2ocv(struct power_supply_battery_info *info,
+				 int dcap, int temp);
 extern int
 power_supply_temp2resist_simple(struct power_supply_resistance_temp_table *table,
 				int table_len, int temp);
-- 
2.31.1


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

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