rtc: ds1307: store previous charge default per chip

Some RTC's batteries and supercaps were charged by default until now.
In contrast other RTCs allow charging but the driver did not configure
them to do so until now. These must not be charged by default to stay
backwards compatible.

In order to do that, store the charge default per chip.
Signed-off-by: Bastian Krause <bst@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200917183246.19446-7-bst@pengutronix.de

drivers/rtc/rtc-ds1307.c

@@ -195,6 +195,11 @@ struct chip_desc {
 	 * the resistor between Vcc and Vbackup?
 	 */
 	bool			requires_trickle_resistor;
+	/* Some RTC's batteries and supercaps were charged by default, others
+	 * allow charging but were not configured previously to do so.
+	 * Remember this behavior to stay backwards compatible.
+	 */
+	bool			charge_default;
 };
 
 static const struct chip_desc chips[last_ds_type];
@@ -991,6 +996,7 @@ static const struct chip_desc chips[last_ds_type] = {
 		.trickle_charger_reg = 0x10,
 		.do_trickle_setup = &do_trickle_setup_ds1339,
 		.requires_trickle_resistor = true,
+		.charge_default = true,
 	},
 	[ds_1340] = {
 		.century_reg	= DS1307_REG_HOUR,
@@ -999,6 +1005,7 @@ static const struct chip_desc chips[last_ds_type] = {
 		.do_trickle_setup = &do_trickle_setup_ds1339,
 		.trickle_charger_reg = 0x08,
 		.requires_trickle_resistor = true,
+		.charge_default = true,
 	},
 	[ds_1341] = {
 		.century_reg	= DS1307_REG_MONTH,
@@ -1307,7 +1314,7 @@ static u8 ds1307_trickle_init(struct ds1307 *ds1307,
 			      const struct chip_desc *chip)
 {
 	u32 ohms;
-	bool diode = true;
+	bool diode = chip->charge_default;
 
 	if (!chip->do_trickle_setup)
 		return 0;