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

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Message-ID: 
 <TY7PR01MB14818A0C465ABB9E20734893FCDB2A@TY7PR01MB14818.jpnprd01.prod.outlook.com>
Date: Wed, 24 Dec 2025 05:05:30 +0000
From: <nobuhiro.iwamatsu.x90@...l.toshiba>
To: <fredrik.m.olsson@...s.com>, <alexandre.belloni@...tlin.com>,
        <robh@...nel.org>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>
CC: <linux-rtc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <kernel@...s.com>
Subject: RE: [PATCH 3/4] rtc: ds1307: Add Driver for Epson RX8901CE

Hi Fredrik,

> -----Original Message-----
> From: Fredrik M Olsson <fredrik.m.olsson@...s.com>
> Sent: Friday, December 19, 2025 9:11 PM
> To: Alexandre Belloni <alexandre.belloni@...tlin.com>; Rob Herring
> <robh@...nel.org>; Krzysztof Kozlowski <krzk+dt@...nel.org>; Conor Dooley
> <conor+dt@...nel.org>; iwamatsu nobuhiro(岩松 信洋 □ＤＩＴＣ○ＣＰＴ)
> <nobuhiro.iwamatsu.x90@...l.toshiba>
> Cc: linux-rtc@...r.kernel.org; devicetree@...r.kernel.org;
> linux-kernel@...r.kernel.org; Fredrik M Olsson <fredrik.m.olsson@...s.com>;
> kernel@...s.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@...s.com>

Reviewed-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.x90@...l.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