[PATCH 0/4] rtc: ds1307: Add support for Epson RX8901CE

[PATCH 0/4] rtc: ds1307: Add support for Epson RX8901CE

[Fredrik M Olsson]

Add basic support for the Epson RX8901CE RTC.
Datasheet: https://download.epsondevice.com/td/pdf/app/RX8901CE_en.pdf

Also includes a bug fix for an issue with reading the weekday from the
RTC which affects both the existing rx8130 and this rx8901 driver.

Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
---
Fredrik M Olsson (4):
      dt-bindings: rtc: ds1307: Add epson,rx8901
      rtc: ds1307: Fix off-by-one issue with wday for rx8130
      rtc: ds1307: Add Driver for Epson RX8901CE
      rtc: ds1307: Add support for reading RX8901CE battery VL status

 .../devicetree/bindings/rtc/rtc-ds1307.yaml        |   1 +
 drivers/rtc/rtc-ds1307.c                           | 104 ++++++++++++++++++++-
 2 files changed, 102 insertions(+), 3 deletions(-)
---
base-commit: ea1013c1539270e372fc99854bc6e4d94eaeff66
change-id: 20251126-ds1307-rx8901-add-a0fe173093e3

Best regards,
-- 
Fredrik M Olsson <fredrik.m.olsson@axis.com>

[PATCH 1/4] dt-bindings: rtc: ds1307: Add epson,rx8901

[Fredrik M Olsson]

Add compatible string epson,rx8901 for the Epson RX8901CE RTC.

Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
---
 Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml b/Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml
index 98d10e680144..9b2796804f07 100644
--- a/Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml
+++ b/Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml
@@ -31,6 +31,7 @@ properties:
           - epson,rx8025
           - isil,isl12057
           - epson,rx8130
+          - epson,rx8901
 
       - items:
           - enum:

-- 
2.43.0

Re: [PATCH 1/4] dt-bindings: rtc: ds1307: Add epson,rx8901

[Krzysztof Kozlowski]

On Fri, Dec 19, 2025 at 01:10:35PM +0100, Fredrik M Olsson wrote:
> Add compatible string epson,rx8901 for the Epson RX8901CE RTC.
> 
> Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
> ---
>  Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml | 1 +
>  1 file changed, 1 insertion(+)

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>

Best regards,
Krzysztof

RE: [PATCH 1/4] dt-bindings: rtc: ds1307: Add epson,rx8901

[nobuhiro.iwamatsu.x90]

Hi Fredrik,

> -----Original Message-----
> From: Fredrik M Olsson <fredrik.m.olsson@axis.com>
> Sent: Friday, December 19, 2025 9:11 PM
> To: Alexandre Belloni <alexandre.belloni@bootlin.com>; Rob Herring
> <robh@kernel.org>; Krzysztof Kozlowski <krzk+dt@kernel.org>; Conor Dooley
> <conor+dt@kernel.org>; iwamatsu nobuhiro(岩松 信洋 □ＤＩＴＣ○ＣＰＴ)
> <nobuhiro.iwamatsu.x90@mail.toshiba>
> Cc: linux-rtc@vger.kernel.org; devicetree@vger.kernel.org;
> linux-kernel@vger.kernel.org; Fredrik M Olsson <fredrik.m.olsson@axis.com>;
> kernel@axis.com
> Subject: [PATCH 1/4] dt-bindings: rtc: ds1307: Add epson,rx8901
> 
> Add compatible string epson,rx8901 for the Epson RX8901CE RTC.
> 
> Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>

Reviewed-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@mail.toshiba>

Best regards,
  Nobuhiro
> ---
>  Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml
> b/Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml
> index 98d10e680144..9b2796804f07 100644
> --- a/Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml
> +++ b/Documentation/devicetree/bindings/rtc/rtc-ds1307.yaml
> @@ -31,6 +31,7 @@ properties:
>            - epson,rx8025
>            - isil,isl12057
>            - epson,rx8130
> +          - epson,rx8901
> 
>        - items:
>            - enum:
> 
> --
> 2.43.0

[PATCH 2/4] rtc: ds1307: Fix off-by-one issue with wday for rx8130

[Fredrik M Olsson]

The RTC represent each weekday with a individual bit set in the WDAY
register, where the 0th bit represent the first day of the week and the
6th bit represents the last day of the week. For each passed day the
chip performs a rotary-left-shift by one to advance the weekday by one.

The tm_wday field represent weekdays by a value in the range of 0-6.

The fls() function return the bit index of the last bit set. To handle
when there are no bits set it will return 0, and if the 0th bit is set
it will return 1, and if the 1st bit is set it will return 2, and so on.

In order to make the result of the fls() function fall into the expected
range of 0-6 (instead of 1-7) this patch subtracts one from the result
(which matches how the value is written in ds1307_set_time()).

Fixes: 204756f016726 ("rtc: ds1307: Fix wday settings for rx8130")
Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
---
 drivers/rtc/rtc-ds1307.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index 7205c59ff729..bf42c250ea7d 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -308,7 +308,7 @@ static int ds1307_get_time(struct device *dev, struct rtc_time *t)
 	t->tm_hour = bcd2bin(tmp);
 	/* rx8130 is bit position, not BCD */
 	if (ds1307->type == rx_8130)
-		t->tm_wday = fls(regs[DS1307_REG_WDAY] & 0x7f);
+		t->tm_wday = fls(regs[DS1307_REG_WDAY] & 0x7f) - 1;
 	else
 		t->tm_wday = bcd2bin(regs[DS1307_REG_WDAY] & 0x07) - 1;
 	t->tm_mday = bcd2bin(regs[DS1307_REG_MDAY] & 0x3f);

-- 
2.43.0

RE: [PATCH 2/4] rtc: ds1307: Fix off-by-one issue with wday for rx8130

[nobuhiro.iwamatsu.x90]

Hi Fredrik,

> -----Original Message-----
> From: Fredrik M Olsson <fredrik.m.olsson@axis.com>
> Sent: Friday, December 19, 2025 9:11 PM
> To: Alexandre Belloni <alexandre.belloni@bootlin.com>; Rob Herring
> <robh@kernel.org>; Krzysztof Kozlowski <krzk+dt@kernel.org>; Conor Dooley
> <conor+dt@kernel.org>; iwamatsu nobuhiro(岩松 信洋 □ＤＩＴＣ○ＣＰＴ)
> <nobuhiro.iwamatsu.x90@mail.toshiba>
> Cc: linux-rtc@vger.kernel.org; devicetree@vger.kernel.org;
> linux-kernel@vger.kernel.org; Fredrik M Olsson <fredrik.m.olsson@axis.com>;
> kernel@axis.com
> Subject: [PATCH 2/4] rtc: ds1307: Fix off-by-one issue with wday for rx8130
> 
> The RTC represent each weekday with a individual bit set in the WDAY register,
> where the 0th bit represent the first day of the week and the 6th bit represents
> the last day of the week. For each passed day the chip performs a
> rotary-left-shift by one to advance the weekday by one.
> 
> The tm_wday field represent weekdays by a value in the range of 0-6.
> 
> The fls() function return the bit index of the last bit set. To handle when there
> are no bits set it will return 0, and if the 0th bit is set it will return 1, and if the
> 1st bit is set it will return 2, and so on.
> 
> In order to make the result of the fls() function fall into the expected range of
> 0-6 (instead of 1-7) this patch subtracts one from the result (which matches
> how the value is written in ds1307_set_time()).
> 
> Fixes: 204756f016726 ("rtc: ds1307: Fix wday settings for rx8130")
> Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>

Thanks for fixing.

Reviewed-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.x90@mail.toshiba>

Best regards,
  Nobuhiro

> ---
>  drivers/rtc/rtc-ds1307.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c index
> 7205c59ff729..bf42c250ea7d 100644
> --- a/drivers/rtc/rtc-ds1307.c
> +++ b/drivers/rtc/rtc-ds1307.c
> @@ -308,7 +308,7 @@ static int ds1307_get_time(struct device *dev, struct
> rtc_time *t)
>  	t->tm_hour = bcd2bin(tmp);
>  	/* rx8130 is bit position, not BCD */
>  	if (ds1307->type == rx_8130)
> -		t->tm_wday = fls(regs[DS1307_REG_WDAY] & 0x7f);
> +		t->tm_wday = fls(regs[DS1307_REG_WDAY] & 0x7f) - 1;
>  	else
>  		t->tm_wday = bcd2bin(regs[DS1307_REG_WDAY] & 0x07) - 1;
>  	t->tm_mday = bcd2bin(regs[DS1307_REG_MDAY] & 0x3f);
> 
> --
> 2.43.0

[PATCH 3/4] rtc: ds1307: Add Driver for Epson RX8901CE

[Fredrik M Olsson]

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, &regflag);
+		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);

-- 
2.43.0

RE: [PATCH 3/4] rtc: ds1307: Add Driver for Epson RX8901CE

[nobuhiro.iwamatsu.x90]

Hi Fredrik,

> -----Original Message-----
> From: Fredrik M Olsson <fredrik.m.olsson@axis.com>
> Sent: Friday, December 19, 2025 9:11 PM
> To: Alexandre Belloni <alexandre.belloni@bootlin.com>; Rob Herring
> <robh@kernel.org>; Krzysztof Kozlowski <krzk+dt@kernel.org>; Conor Dooley
> <conor+dt@kernel.org>; iwamatsu nobuhiro(岩松 信洋 □ＤＩＴＣ○ＣＰＴ)
> <nobuhiro.iwamatsu.x90@mail.toshiba>
> Cc: linux-rtc@vger.kernel.org; devicetree@vger.kernel.org;
> linux-kernel@vger.kernel.org; Fredrik M Olsson <fredrik.m.olsson@axis.com>;
> kernel@axis.com
> Subject: [PATCH 3/4] rtc: ds1307: Add Driver for Epson RX8901CE
> 
> 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>

Reviewed-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.x90@mail.toshiba>

Best regards,
  Nobuhiro

> ---
>  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,
> &regflag);
> +		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);
> 
> --
> 2.43.0

Re: [PATCH 3/4] rtc: ds1307: Add Driver for Epson RX8901CE

[Alexandre Belloni]

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, &regflag);
> +		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

Re: [PATCH 3/4] rtc: ds1307: Add Driver for Epson RX8901CE

[Fredrik M Olsson]

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, &regflag);
>> +             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

[PATCH 4/4] rtc: ds1307: Add support for reading RX8901CE battery VL status

[Fredrik M Olsson]

Adds support for:
- Reading the battery voltage low status using the RTC_VL_READ ioctl,
  which also reports invalid time information if the VLF flag is set.

Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
---
 drivers/rtc/rtc-ds1307.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index 99d95e520108..ca062ed0c867 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -133,8 +133,11 @@ enum ds_type {
 #define RX8901_REG_INTF			0x0e
 #define RX8901_REG_INTF_VLF		BIT(1)
 #define RX8901_REG_PWSW_CFG		0x37
+#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 MCP794XX_REG_CONTROL		0x07
 #	define MCP794XX_BIT_ALM0_EN	0x10
@@ -458,6 +461,39 @@ static int ds1307_set_time(struct device *dev, struct rtc_time *t)
 	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, &regflag);
+		if (ret)
+			return ret;
+
+		if (regflag & RX8901_REG_INTF_VLF)
+			tmp |= RTC_VL_DATA_INVALID;
+
+		ret = regmap_read(ds1307->regmap, RX8901_REG_BUF_INTF, &regflag);
+		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;
+}
+#else
+#define rx8901_ioctl NULL
+#endif
+
 static int ds1337_read_alarm(struct device *dev, struct rtc_wkalrm *t)
 {
 	struct ds1307		*ds1307 = dev_get_drvdata(dev);
@@ -599,10 +635,13 @@ 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)
+static u8 do_trickle_setup_rx8901(struct ds1307 *ds1307, u32 ohms __always_unused, bool diode)
 {
-	/* make sure that the backup battery is enabled */
-	u8 setup = RX8901_REG_PWSW_CFG_INIEN;
+	/*
+	 * make sure that the backup battery is enabled and that battery
+	 * voltage detection is performed
+	 */
+	u8 setup = RX8901_REG_PWSW_CFG_INIEN | RX8901_REG_PWSW_CFG_VBATLDETEN;
 
 	if (diode)
 		setup |= RX8901_REG_PWSW_CFG_CHGEN;
@@ -1005,6 +1044,7 @@ static const struct rtc_class_ops rx8130_rtc_ops = {
 static const struct rtc_class_ops rx8901_rtc_ops = {
 	.read_time      = ds1307_get_time,
 	.set_time       = ds1307_set_time,
+	.ioctl          = rx8901_ioctl,
 };
 
 static const struct rtc_class_ops mcp794xx_rtc_ops = {

-- 
2.43.0

RE: [PATCH 4/4] rtc: ds1307: Add support for reading RX8901CE battery VL status

[nobuhiro.iwamatsu.x90]

Hi Fredrik,

> -----Original Message-----
> From: Fredrik M Olsson <fredrik.m.olsson@axis.com>
> Sent: Friday, December 19, 2025 9:11 PM
> To: Alexandre Belloni <alexandre.belloni@bootlin.com>; Rob Herring
> <robh@kernel.org>; Krzysztof Kozlowski <krzk+dt@kernel.org>; Conor Dooley
> <conor+dt@kernel.org>; iwamatsu nobuhiro(岩松 信洋 □ＤＩＴＣ○ＣＰＴ)
> <nobuhiro.iwamatsu.x90@mail.toshiba>
> Cc: linux-rtc@vger.kernel.org; devicetree@vger.kernel.org;
> linux-kernel@vger.kernel.org; Fredrik M Olsson <fredrik.m.olsson@axis.com>;
> kernel@axis.com
> Subject: [PATCH 4/4] rtc: ds1307: Add support for reading RX8901CE battery
> VL status
> 
> Adds support for:
> - Reading the battery voltage low status using the RTC_VL_READ ioctl,
>   which also reports invalid time information if the VLF flag is set.
> 
> Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>

Reviewed-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.x90@mail.toshiba>

Best regards,
  Nobuhiro

> ---
>  drivers/rtc/rtc-ds1307.c | 46
> +++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 43 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c index
> 99d95e520108..ca062ed0c867 100644
> --- a/drivers/rtc/rtc-ds1307.c
> +++ b/drivers/rtc/rtc-ds1307.c
> @@ -133,8 +133,11 @@ enum ds_type {
>  #define RX8901_REG_INTF			0x0e
>  #define RX8901_REG_INTF_VLF		BIT(1)
>  #define RX8901_REG_PWSW_CFG		0x37
> +#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 MCP794XX_REG_CONTROL		0x07
>  #	define MCP794XX_BIT_ALM0_EN	0x10
> @@ -458,6 +461,39 @@ static int ds1307_set_time(struct device *dev, struct
> rtc_time *t)
>  	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,
> &regflag);
> +		if (ret)
> +			return ret;
> +
> +		if (regflag & RX8901_REG_INTF_VLF)
> +			tmp |= RTC_VL_DATA_INVALID;
> +
> +		ret = regmap_read(ds1307->regmap, RX8901_REG_BUF_INTF,
> &regflag);
> +		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;
> +}
> +#else
> +#define rx8901_ioctl NULL
> +#endif
> +
>  static int ds1337_read_alarm(struct device *dev, struct rtc_wkalrm *t)  {
>  	struct ds1307		*ds1307 = dev_get_drvdata(dev);
> @@ -599,10 +635,13 @@ 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)
> +static u8 do_trickle_setup_rx8901(struct ds1307 *ds1307, u32 ohms
> +__always_unused, bool diode)
>  {
> -	/* make sure that the backup battery is enabled */
> -	u8 setup = RX8901_REG_PWSW_CFG_INIEN;
> +	/*
> +	 * make sure that the backup battery is enabled and that battery
> +	 * voltage detection is performed
> +	 */
> +	u8 setup = RX8901_REG_PWSW_CFG_INIEN |
> RX8901_REG_PWSW_CFG_VBATLDETEN;
> 
>  	if (diode)
>  		setup |= RX8901_REG_PWSW_CFG_CHGEN;
> @@ -1005,6 +1044,7 @@ static const struct rtc_class_ops rx8130_rtc_ops =
> {  static const struct rtc_class_ops rx8901_rtc_ops = {
>  	.read_time      = ds1307_get_time,
>  	.set_time       = ds1307_set_time,
> +	.ioctl          = rx8901_ioctl,
>  };
> 
>  static const struct rtc_class_ops mcp794xx_rtc_ops = {
> 
> --
> 2.43.0

Re: [PATCH 4/4] rtc: ds1307: Add support for reading RX8901CE battery VL status

[Alexandre Belloni]

On 19/12/2025 13:10:38+0100, Fredrik M Olsson wrote:
> Adds support for:
> - Reading the battery voltage low status using the RTC_VL_READ ioctl,
>   which also reports invalid time information if the VLF flag is set.
> 
> Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
> ---
>  drivers/rtc/rtc-ds1307.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 43 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
> index 99d95e520108..ca062ed0c867 100644
> --- a/drivers/rtc/rtc-ds1307.c
> +++ b/drivers/rtc/rtc-ds1307.c
> @@ -133,8 +133,11 @@ enum ds_type {
>  #define RX8901_REG_INTF			0x0e
>  #define RX8901_REG_INTF_VLF		BIT(1)
>  #define RX8901_REG_PWSW_CFG		0x37
> +#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 MCP794XX_REG_CONTROL		0x07
>  #	define MCP794XX_BIT_ALM0_EN	0x10
> @@ -458,6 +461,39 @@ static int ds1307_set_time(struct device *dev, struct rtc_time *t)
>  	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, &regflag);
> +		if (ret)
> +			return ret;
> +
> +		if (regflag & RX8901_REG_INTF_VLF)
> +			tmp |= RTC_VL_DATA_INVALID;
> +
> +		ret = regmap_read(ds1307->regmap, RX8901_REG_BUF_INTF, &regflag);
> +		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;
> +}
> +#else
> +#define rx8901_ioctl NULL
> +#endif
> +
>  static int ds1337_read_alarm(struct device *dev, struct rtc_wkalrm *t)
>  {
>  	struct ds1307		*ds1307 = dev_get_drvdata(dev);
> @@ -599,10 +635,13 @@ 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)
> +static u8 do_trickle_setup_rx8901(struct ds1307 *ds1307, u32 ohms __always_unused, bool diode)
>  {
> -	/* make sure that the backup battery is enabled */
> -	u8 setup = RX8901_REG_PWSW_CFG_INIEN;
> +	/*
> +	 * make sure that the backup battery is enabled and that battery
> +	 * voltage detection is performed
> +	 */
> +	u8 setup = RX8901_REG_PWSW_CFG_INIEN | RX8901_REG_PWSW_CFG_VBATLDETEN;
>  
>  	if (diode)
>  		setup |= RX8901_REG_PWSW_CFG_CHGEN;
> @@ -1005,6 +1044,7 @@ static const struct rtc_class_ops rx8130_rtc_ops = {
>  static const struct rtc_class_ops rx8901_rtc_ops = {
>  	.read_time      = ds1307_get_time,
>  	.set_time       = ds1307_set_time,
> +	.ioctl          = rx8901_ioctl,
>  };
>  

This seems to be an unrelated changed that hasn't been squashed in the
proper patch.


-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH 4/4] rtc: ds1307: Add support for reading RX8901CE battery VL status

[Fredrik M Olsson]

On 1/31/26 01:05, 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 ]
> 
> On 19/12/2025 13:10:38+0100, Fredrik M Olsson wrote:
>> Adds support for:
>> - Reading the battery voltage low status using the RTC_VL_READ ioctl,
>>    which also reports invalid time information if the VLF flag is set.
>>
>> Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
>> ---
>>   drivers/rtc/rtc-ds1307.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
>>   1 file changed, 43 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
>> index 99d95e520108..ca062ed0c867 100644
>> --- a/drivers/rtc/rtc-ds1307.c
>> +++ b/drivers/rtc/rtc-ds1307.c
>> @@ -133,8 +133,11 @@ enum ds_type {
>>   #define RX8901_REG_INTF                      0x0e
>>   #define RX8901_REG_INTF_VLF          BIT(1)
>>   #define RX8901_REG_PWSW_CFG          0x37
>> +#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 MCP794XX_REG_CONTROL         0x07
>>   #    define MCP794XX_BIT_ALM0_EN     0x10
>> @@ -458,6 +461,39 @@ static int ds1307_set_time(struct device *dev, struct rtc_time *t)
>>        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, &regflag);
>> +             if (ret)
>> +                     return ret;
>> +
>> +             if (regflag & RX8901_REG_INTF_VLF)
>> +                     tmp |= RTC_VL_DATA_INVALID;
>> +
>> +             ret = regmap_read(ds1307->regmap, RX8901_REG_BUF_INTF, &regflag);
>> +             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;
>> +}
>> +#else
>> +#define rx8901_ioctl NULL
>> +#endif
>> +
>>   static int ds1337_read_alarm(struct device *dev, struct rtc_wkalrm *t)
>>   {
>>        struct ds1307           *ds1307 = dev_get_drvdata(dev);
>> @@ -599,10 +635,13 @@ 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)
>> +static u8 do_trickle_setup_rx8901(struct ds1307 *ds1307, u32 ohms __always_unused, bool diode)
>>   {
>> -     /* make sure that the backup battery is enabled */
>> -     u8 setup = RX8901_REG_PWSW_CFG_INIEN;
>> +     /*
>> +      * make sure that the backup battery is enabled and that battery
>> +      * voltage detection is performed
>> +      */
>> +     u8 setup = RX8901_REG_PWSW_CFG_INIEN | RX8901_REG_PWSW_CFG_VBATLDETEN;
>>
>>        if (diode)
>>                setup |= RX8901_REG_PWSW_CFG_CHGEN;
>> @@ -1005,6 +1044,7 @@ static const struct rtc_class_ops rx8130_rtc_ops = {
>>   static const struct rtc_class_ops rx8901_rtc_ops = {
>>        .read_time      = ds1307_get_time,
>>        .set_time       = ds1307_set_time,
>> +     .ioctl          = rx8901_ioctl,
>>   };
>>
> 
> This seems to be an unrelated changed that hasn't been squashed in the
> proper patch.
> 

Okay I will squash this change into patch 3 for v2.

> 
> --
> Alexandre Belloni, co-owner and COO, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com


-- 
/Fredrik