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@xxxxxxxx>
> Sent: Friday, December 19, 2025 9:11 PM
> To: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>; Rob Herring
> <robh@xxxxxxxxxx>; Krzysztof Kozlowski <krzk+dt@xxxxxxxxxx>; Conor Dooley
> <conor+dt@xxxxxxxxxx>; iwamatsu nobuhiro(岩松 信洋 □ＤＩＴＣ○ＣＰＴ)
> <nobuhiro.iwamatsu.x90@mail.toshiba>
> Cc: linux-rtc@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Fredrik M Olsson <fredrik.m.olsson@xxxxxxxx>;
> kernel@xxxxxxxx
> 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@xxxxxxxx>

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