[PATCH v2 3/3] rtc: ds1307: Add driver for Epson RX8901CE
From: Fredrik M Olsson
Date: Wed May 20 2026 - 11:12:02 EST
Adds support for:
- Reading and writing time to/from the RTC.
- Changing Backup Switch Mode (BSM) to DISABLED/DIRECT/LEVEL using the
RTC_PARAM_SET ioctl.
- Optionally enabling battery charging.
- Reading the battery voltage low status using the RTC_VL_READ ioctl
(only supported in LEVEL BSM), which also reports invalid time
information if the VLF flag is set.
Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@xxxxxxxx>
---
drivers/rtc/rtc-ds1307.c | 216 +++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 207 insertions(+), 9 deletions(-)
diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index bf42c250ea7d..23dd104aa2be 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -9,6 +9,7 @@
*/
#include <linux/bcd.h>
+#include <linux/bitfield.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kstrtox.h>
@@ -48,6 +49,7 @@ enum ds_type {
mcp794xx,
rx_8025,
rx_8130,
+ rx_8901,
last_ds_type /* always last */
/* rs5c372 too? different address... */
};
@@ -129,6 +131,18 @@ enum ds_type {
#define RX8130_REG_CONTROL1_INIEN BIT(4)
#define RX8130_REG_CONTROL1_CHGEN BIT(5)
+#define RX8901_REG_INTF 0x0e
+#define RX8901_REG_INTF_VLF BIT(1)
+#define RX8901_REG_PWSW_CFG 0x37
+#define RX8901_REG_PWSW_CFG_SWSEL GENMASK(3, 2)
+#define RX8901_REG_PWSW_CFG_VBATLDETEN BIT(4)
+#define RX8901_REG_PWSW_CFG_INIEN BIT(6)
+#define RX8901_REG_PWSW_CFG_CHGEN BIT(7)
+#define RX8901_REG_BUF_INTF 0x46
+#define RX8901_REG_BUF_INTF_VBATLF BIT(3)
+#define RX8901_SWSEL_PRIMARY_BACKUP 0x1
+#define RX8901_SWSEL_PRIMARY 0x2
+
#define MCP794XX_REG_CONTROL 0x07
# define MCP794XX_BIT_ALM0_EN 0x10
# define MCP794XX_BIT_ALM1_EN 0x20
@@ -192,8 +206,8 @@ struct chip_desc {
irq_handler_t irq_handler;
const struct rtc_class_ops *rtc_ops;
u16 trickle_charger_reg;
- u8 (*do_trickle_setup)(struct ds1307 *, u32,
- bool);
+ int (*do_trickle_setup)(struct ds1307 *ds1307, u32 ohms,
+ bool diode);
/* Does the RTC require trickle-resistor-ohms to select the value of
* the resistor between Vcc and Vbackup?
*/
@@ -216,6 +230,7 @@ static int ds1307_get_time(struct device *dev, struct rtc_time *t)
if (ds1307->type == rx_8130) {
unsigned int regflag;
+
ret = regmap_read(ds1307->regmap, RX8130_REG_FLAG, ®flag);
if (ret) {
dev_err(dev, "%s error %d\n", "read", ret);
@@ -226,6 +241,19 @@ static int ds1307_get_time(struct device *dev, struct rtc_time *t)
dev_warn_once(dev, "oscillator failed, set time!\n");
return -EINVAL;
}
+ } else if (ds1307->type == rx_8901) {
+ unsigned int regflag;
+
+ ret = regmap_read(ds1307->regmap, RX8901_REG_INTF, ®flag);
+ if (ret) {
+ dev_dbg(dev, "%s error %d\n", "read", ret);
+ return ret;
+ }
+
+ if (regflag & RX8901_REG_INTF_VLF) {
+ dev_warn_once(dev, "oscillator failed, set time!\n");
+ return -EINVAL;
+ }
}
/* read the RTC date and time registers all at once */
@@ -307,7 +335,7 @@ static int ds1307_get_time(struct device *dev, struct rtc_time *t)
tmp = regs[DS1307_REG_HOUR] & 0x3f;
t->tm_hour = bcd2bin(tmp);
/* rx8130 is bit position, not BCD */
- if (ds1307->type == rx_8130)
+ if (ds1307->type == rx_8130 || ds1307->type == rx_8901)
t->tm_wday = fls(regs[DS1307_REG_WDAY] & 0x7f) - 1;
else
t->tm_wday = bcd2bin(regs[DS1307_REG_WDAY] & 0x07) - 1;
@@ -358,7 +386,7 @@ static int ds1307_set_time(struct device *dev, struct rtc_time *t)
regs[DS1307_REG_MIN] = bin2bcd(t->tm_min);
regs[DS1307_REG_HOUR] = bin2bcd(t->tm_hour);
/* rx8130 is bit position, not BCD */
- if (ds1307->type == rx_8130)
+ if (ds1307->type == rx_8130 || ds1307->type == rx_8901)
regs[DS1307_REG_WDAY] = 1 << t->tm_wday;
else
regs[DS1307_REG_WDAY] = bin2bcd(t->tm_wday + 1);
@@ -422,11 +450,132 @@ static int ds1307_set_time(struct device *dev, struct rtc_time *t)
dev_err(dev, "%s error %d\n", "write", result);
return result;
}
+ } else if (ds1307->type == rx_8901) {
+ /*
+ * clear Voltage Loss Flag as data is available now (writing 1
+ * to the other bits in the INTF register has no effect)
+ */
+ result = regmap_write(ds1307->regmap, RX8901_REG_INTF,
+ 0xff ^ RX8901_REG_INTF_VLF);
+ if (result) {
+ dev_dbg(dev, "%s error %d\n", "write", result);
+ return result;
+ }
}
return 0;
}
+#ifdef CONFIG_RTC_INTF_DEV
+static int rx8901_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
+{
+ struct ds1307 *ds1307 = dev_get_drvdata(dev);
+ unsigned int regflag, tmp = 0;
+ int ret = 0;
+
+ switch (cmd) {
+ case RTC_VL_READ:
+ ret = regmap_read(ds1307->regmap, RX8901_REG_INTF, ®flag);
+ if (ret)
+ return ret;
+
+ if (regflag & RX8901_REG_INTF_VLF)
+ tmp |= RTC_VL_DATA_INVALID;
+
+ ret = regmap_read(ds1307->regmap, RX8901_REG_BUF_INTF, ®flag);
+ if (ret)
+ return ret;
+
+ if (regflag & RX8901_REG_BUF_INTF_VBATLF)
+ tmp |= RTC_VL_BACKUP_LOW;
+
+ return put_user(tmp, (unsigned int __user *)arg);
+ default:
+ return -ENOIOCTLCMD;
+ }
+ return ret;
+}
+
+static int rx8901_param_get(struct device *dev, struct rtc_param *param)
+{
+ struct ds1307 *ds1307 = dev_get_drvdata(dev);
+ unsigned int regflag;
+ int ret;
+
+ switch (param->param) {
+ case RTC_PARAM_BACKUP_SWITCH_MODE:
+ ret = regmap_read(ds1307->regmap, RX8901_REG_PWSW_CFG, ®flag);
+ if (ret)
+ return ret;
+
+ if (regflag & RX8901_REG_PWSW_CFG_INIEN) {
+ param->uvalue = RTC_BSM_LEVEL;
+ } else {
+ unsigned int swsel = FIELD_GET(RX8901_REG_PWSW_CFG_SWSEL, regflag);
+
+ if (swsel == RX8901_SWSEL_PRIMARY_BACKUP)
+ param->uvalue = RTC_BSM_DIRECT;
+ else
+ param->uvalue = RTC_BSM_DISABLED;
+ }
+
+ break;
+
+ default:
+ return -EINVAL;
+ }
+ return ret;
+}
+
+static int rx8901_param_set(struct device *dev, struct rtc_param *param)
+{
+ struct ds1307 *ds1307 = dev_get_drvdata(dev);
+ unsigned int regmask;
+ unsigned int regval;
+ int ret;
+
+ switch (param->param) {
+ case RTC_PARAM_BACKUP_SWITCH_MODE:
+
+ switch (param->uvalue) {
+ case RTC_BSM_DISABLED:
+ /* Only main power supply is used */
+ regmask = RX8901_REG_PWSW_CFG_INIEN |
+ RX8901_REG_PWSW_CFG_SWSEL;
+ regval = FIELD_PREP(RX8901_REG_PWSW_CFG_SWSEL,
+ RX8901_SWSEL_PRIMARY) |
+ FIELD_PREP(RX8901_REG_PWSW_CFG_INIEN, 0);
+ break;
+ case RTC_BSM_DIRECT:
+ /* Main and battery power supply is put in parallel (default) */
+ regmask = RX8901_REG_PWSW_CFG_INIEN |
+ RX8901_REG_PWSW_CFG_SWSEL;
+ regval = FIELD_PREP(RX8901_REG_PWSW_CFG_SWSEL,
+ RX8901_SWSEL_PRIMARY_BACKUP) |
+ FIELD_PREP(RX8901_REG_PWSW_CFG_INIEN, 0);
+ break;
+ case RTC_BSM_LEVEL:
+ /* Enable auto power switching between main and backup power supply */
+ regmask = RX8901_REG_PWSW_CFG_INIEN;
+ regval = FIELD_PREP(RX8901_REG_PWSW_CFG_INIEN, 1);
+ break;
+ default:
+ return -EINVAL;
+ }
+ ret = regmap_update_bits(ds1307->regmap, RX8901_REG_PWSW_CFG, regmask, regval);
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return ret;
+}
+#else
+#define rx8901_ioctl NULL
+#define rx8901_param_get NULL
+#define rx8901_param_set NULL
+#endif
+
static int ds1337_read_alarm(struct device *dev, struct rtc_wkalrm *t)
{
struct ds1307 *ds1307 = dev_get_drvdata(dev);
@@ -533,7 +682,7 @@ static int ds1307_alarm_irq_enable(struct device *dev, unsigned int enabled)
enabled ? DS1337_BIT_A1IE : 0);
}
-static u8 do_trickle_setup_ds1339(struct ds1307 *ds1307, u32 ohms, bool diode)
+static int do_trickle_setup_ds1339(struct ds1307 *ds1307, u32 ohms, bool diode)
{
u8 setup = (diode) ? DS1307_TRICKLE_CHARGER_DIODE :
DS1307_TRICKLE_CHARGER_NO_DIODE;
@@ -558,7 +707,7 @@ static u8 do_trickle_setup_ds1339(struct ds1307 *ds1307, u32 ohms, bool diode)
return setup;
}
-static u8 do_trickle_setup_rx8130(struct ds1307 *ds1307, u32 ohms, bool diode)
+static int do_trickle_setup_rx8130(struct ds1307 *ds1307, u32 ohms, bool diode)
{
/* make sure that the backup battery is enabled */
u8 setup = RX8130_REG_CONTROL1_INIEN;
@@ -568,6 +717,26 @@ static u8 do_trickle_setup_rx8130(struct ds1307 *ds1307, u32 ohms, bool diode)
return setup;
}
+static int do_trickle_setup_rx8901(struct ds1307 *ds1307, u32 ohms __always_unused, bool diode)
+{
+ int ret;
+ unsigned int setup;
+
+ ret = regmap_read(ds1307->regmap, RX8901_REG_PWSW_CFG, &setup);
+ if (ret) {
+ dev_err(ds1307->dev, "Failed to read PWSW_CFG register\n");
+ return ret;
+ }
+
+ /* Enable low battery voltage detection */
+ setup |= RX8901_REG_PWSW_CFG_VBATLDETEN;
+
+ if (diode)
+ setup |= RX8901_REG_PWSW_CFG_CHGEN;
+
+ return setup;
+}
+
static irqreturn_t rx8130_irq(int irq, void *dev_id)
{
struct ds1307 *ds1307 = dev_id;
@@ -960,6 +1129,14 @@ static const struct rtc_class_ops rx8130_rtc_ops = {
.alarm_irq_enable = rx8130_alarm_irq_enable,
};
+static const struct rtc_class_ops rx8901_rtc_ops = {
+ .read_time = ds1307_get_time,
+ .set_time = ds1307_set_time,
+ .ioctl = rx8901_ioctl,
+ .param_get = rx8901_param_get,
+ .param_set = rx8901_param_set,
+};
+
static const struct rtc_class_ops mcp794xx_rtc_ops = {
.read_time = ds1307_get_time,
.set_time = ds1307_set_time,
@@ -1040,6 +1217,12 @@ static const struct chip_desc chips[last_ds_type] = {
.trickle_charger_reg = RX8130_REG_CONTROL1,
.do_trickle_setup = &do_trickle_setup_rx8130,
},
+ [rx_8901] = {
+ .offset = 0x0,
+ .rtc_ops = &rx8901_rtc_ops,
+ .trickle_charger_reg = RX8901_REG_PWSW_CFG,
+ .do_trickle_setup = &do_trickle_setup_rx8901,
+ },
[m41t0] = {
.rtc_ops = &m41txx_rtc_ops,
},
@@ -1081,6 +1264,7 @@ static const struct i2c_device_id ds1307_id[] = {
{ "rx8025", rx_8025 },
{ "isl12057", ds_1337 },
{ "rx8130", rx_8130 },
+ { "rx8901", rx_8901 },
{ }
};
MODULE_DEVICE_TABLE(i2c, ds1307_id);
@@ -1158,6 +1342,10 @@ static const struct of_device_id ds1307_of_match[] = {
.compatible = "epson,rx8130",
.data = (void *)rx_8130
},
+ {
+ .compatible = "epson,rx8901",
+ .data = (void *)rx_8901
+ },
{ }
};
MODULE_DEVICE_TABLE(of, ds1307_of_match);
@@ -1292,7 +1480,7 @@ static int ds1307_nvram_write(void *priv, unsigned int offset, void *val,
/*----------------------------------------------------------------------*/
-static u8 ds1307_trickle_init(struct ds1307 *ds1307,
+static int ds1307_trickle_init(struct ds1307 *ds1307,
const struct chip_desc *chip)
{
u32 ohms, chargeable;
@@ -1745,7 +1933,7 @@ static int ds1307_probe(struct i2c_client *client)
bool ds1307_can_wakeup_device = false;
unsigned char regs[8];
struct ds1307_platform_data *pdata = dev_get_platdata(&client->dev);
- u8 trickle_charger_setup = 0;
+ int trickle_charger_setup = 0;
ds1307 = devm_kzalloc(&client->dev, sizeof(struct ds1307), GFP_KERNEL);
if (!ds1307)
@@ -1781,12 +1969,15 @@ static int ds1307_probe(struct i2c_client *client)
else if (pdata->trickle_charger_setup)
trickle_charger_setup = pdata->trickle_charger_setup;
+ if (trickle_charger_setup < 0)
+ return trickle_charger_setup;
+
if (trickle_charger_setup && chip->trickle_charger_reg) {
dev_dbg(ds1307->dev,
"writing trickle charger info 0x%x to 0x%x\n",
trickle_charger_setup, chip->trickle_charger_reg);
regmap_write(ds1307->regmap, chip->trickle_charger_reg,
- trickle_charger_setup);
+ (u8)trickle_charger_setup);
}
/*
@@ -1990,6 +2181,13 @@ static int ds1307_probe(struct i2c_client *client)
}
}
+ switch (ds1307->type) {
+ case rx_8901:
+ set_bit(RTC_FEATURE_BACKUP_SWITCH_MODE, ds1307->rtc->features);
+ break;
+ default:
+ }
+
ds1307->rtc->ops = chip->rtc_ops ?: &ds13xx_rtc_ops;
err = ds1307_add_frequency_test(ds1307);
if (err)
--
2.43.0