linux-kernel - Re: [PATCH 5/8] rtc: isl12022: implement RTC_VL_READ and RTC_VL

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Date:   Mon, 12 Jun 2023 16:07:46 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] rtc: isl12022: implement RTC_VL_READ and RTC_VL_CLR
 ioctls

On 12/06/2023 13:30:55+0200, Rasmus Villemoes wrote:
> Hook up support for reading the values of the SR_LBAT85 and SR_LBAT75
> bits. Translate the former to "battery low", and the latter to
> "battery empty or not-present".
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  drivers/rtc/rtc-isl12022.c | 41 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)
> 
> diff --git a/drivers/rtc/rtc-isl12022.c b/drivers/rtc/rtc-isl12022.c
> index cb8f1d92e116..1b6659a9b33a 100644
> --- a/drivers/rtc/rtc-isl12022.c
> +++ b/drivers/rtc/rtc-isl12022.c
> @@ -203,7 +203,48 @@ static int isl12022_rtc_set_time(struct device *dev, struct rtc_time *tm)
>  	return regmap_bulk_write(regmap, ISL12022_REG_SC, buf, sizeof(buf));
>  }
>  
> +static int isl12022_read_sr(struct regmap *regmap)
> +{
> +	int ret;
> +	u32 val;
> +
> +	ret = regmap_read(regmap, ISL12022_REG_SR, &val);
> +	if (ret < 0)
> +		return ret;
> +	return val;
> +}
> +
> +static int isl12022_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
> +{
> +	struct regmap *regmap = dev_get_drvdata(dev);
> +	u32 user = 0;
> +	int ret;
> +
> +	switch (cmd) {
> +	case RTC_VL_READ:
> +		ret = isl12022_read_sr(regmap);
> +		if (ret < 0)
> +			return ret;
> +
> +		if (ret & ISL12022_SR_LBAT85)
> +			user |= RTC_VL_BACKUP_LOW;
> +
> +		if (ret & ISL12022_SR_LBAT75)
> +			user |= RTC_VL_BACKUP_EMPTY;
> +
> +		return put_user(user, (u32 __user *)arg);
> +
> +	case RTC_VL_CLR:
> +		return regmap_clear_bits(regmap, ISL12022_REG_SR,
> +					 ISL12022_SR_LBAT85 | ISL12022_SR_LBAT75);

I'm against using RTC_VL_CLR for this as it deletes important
information (i.e. the date is probably invalid). You should let the RTC
clear the bits once the battery has been changed:

"The LBAT75 bit is set when the
VBAT has dropped below the pre-selected trip level, and will self
clear when the VBAT is above the pre-selected trip level at the
next detection cycle either by manual or automatic trigger."

> +
> +	default:
> +		return -ENOIOCTLCMD;
> +	}
> +}
> +
>  static const struct rtc_class_ops isl12022_rtc_ops = {
> +	.ioctl		= isl12022_rtc_ioctl,
>  	.read_time	= isl12022_rtc_read_time,
>  	.set_time	= isl12022_rtc_set_time,
>  };
> -- 
> 2.37.2
> 

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