Adds Support for:
- Reading and writing time to/from the RTC.
- Switching to backup battery supply when primary supply disappears.
- Optionally enabling battery charging.
Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
---
drivers/rtc/rtc-ds1307.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 60 insertions(+), 2 deletions(-)
diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index bf42c250ea7d..99d95e520108 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -48,6 +48,7 @@ enum ds_type {
mcp794xx,
rx_8025,
rx_8130,
+ rx_8901,
last_ds_type /* always last */
/* rs5c372 too? different address... */
};
@@ -129,6 +130,12 @@ 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_INIEN BIT(6)
+#define RX8901_REG_PWSW_CFG_CHGEN BIT(7)
+
#define MCP794XX_REG_CONTROL 0x07
# define MCP794XX_BIT_ALM0_EN 0x10
# define MCP794XX_BIT_ALM1_EN 0x20
@@ -226,6 +233,19 @@ 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_err(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 +327,7 @@ 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 +378,7 @@ 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);
@@ -422,6 +442,17 @@ 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_err(dev, "%s error %d\n", "write", result);
+ return result;
+ }
}
return 0;
@@ -568,6 +599,17 @@ static u8 do_trickle_setup_rx8130(struct ds1307 *ds1307, u32 ohms, bool diode)
return setup;
}
+static u8 do_trickle_setup_rx8901(struct ds1307 *ds1307, u32 ohms, bool diode)
+{
+ /* make sure that the backup battery is enabled */
+ u8 setup = RX8901_REG_PWSW_CFG_INIEN;
+
+ 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 +1002,11 @@ 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,
+};
+
static const struct rtc_class_ops mcp794xx_rtc_ops = {
.read_time = ds1307_get_time,
.set_time = ds1307_set_time,
@@ -1040,6 +1087,12 @@ 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 +1134,7 @@ 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 +1212,10 @@ 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);
--
2.43.0Hello,
On 19/12/2025 13:10:37+0100, Fredrik M Olsson wrote:
> #define MCP794XX_REG_CONTROL 0x07
> # define MCP794XX_BIT_ALM0_EN 0x10
> # define MCP794XX_BIT_ALM1_EN 0x20
> @@ -226,6 +233,19 @@ 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_err(dev, "%s error %d\n", "read", ret);
The multiple dev_err you are adding should be dev_dbg as there is no
other actions for the user than to restart the operation when it fails
so there is not actual value apart when debugging.
> + 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 +327,7 @@ 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 +378,7 @@ 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);
> @@ -422,6 +442,17 @@ 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_err(dev, "%s error %d\n", "write", result);
> + return result;
> + }
> }
>
> return 0;
> @@ -568,6 +599,17 @@ static u8 do_trickle_setup_rx8130(struct ds1307 *ds1307, u32 ohms, bool diode)
> return setup;
> }
>
> +static u8 do_trickle_setup_rx8901(struct ds1307 *ds1307, u32 ohms, bool diode)
> +{
> + /* make sure that the backup battery is enabled */
> + u8 setup = RX8901_REG_PWSW_CFG_INIEN;
You can't do this as this will cause issues in the future for people
wanting to keep this bit disabled (the main reason being that you don't
want to draw power from the battery while your device sits on a shelf).
You have to handle the RTC_PARAM_BACKUP_SWITCH_MODE parameter and then
switch it from userspace.
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
On 1/31/26 01:03, Alexandre Belloni wrote:
> [Some people who received this message don't often get email from alexandre.belloni@bootlin.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> Hello,
>
> On 19/12/2025 13:10:37+0100, Fredrik M Olsson wrote:
>> #define MCP794XX_REG_CONTROL 0x07
>> # define MCP794XX_BIT_ALM0_EN 0x10
>> # define MCP794XX_BIT_ALM1_EN 0x20
>> @@ -226,6 +233,19 @@ 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_err(dev, "%s error %d\n", "read", ret);
>
> The multiple dev_err you are adding should be dev_dbg as there is no
> other actions for the user than to restart the operation when it fails
> so there is not actual value apart when debugging.
>
Okay thanks I will update that for v2.
>> + 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 +327,7 @@ 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 +378,7 @@ 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);
>> @@ -422,6 +442,17 @@ 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_err(dev, "%s error %d\n", "write", result);
>> + return result;
>> + }
>> }
>>
>> return 0;
>> @@ -568,6 +599,17 @@ static u8 do_trickle_setup_rx8130(struct ds1307 *ds1307, u32 ohms, bool diode)
>> return setup;
>> }
>>
>> +static u8 do_trickle_setup_rx8901(struct ds1307 *ds1307, u32 ohms, bool diode)
>> +{
>> + /* make sure that the backup battery is enabled */
>> + u8 setup = RX8901_REG_PWSW_CFG_INIEN;
>
> You can't do this as this will cause issues in the future for people
> wanting to keep this bit disabled (the main reason being that you don't
> want to draw power from the battery while your device sits on a shelf).
> You have to handle the RTC_PARAM_BACKUP_SWITCH_MODE parameter and then
> switch it from userspace.
Here my intention was to do something similar to what was done before
for the rx8130 device [1], which as I understand it require similar
setup initialization as the rx8901 device does. Is using the
RTC_PARAM_BACKUP_SWITCH_MODE the new way of performing this initialization?
>
>
> --
> Alexandre Belloni, co-owner and COO, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
[1] 0026f1604c9b (rtc: ds1307: enable rx8130's backup battery, make it
chargeable optionally)
--
/Fredrik
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