linux-kernel - Re: [PATCH v8 5/8] rtc: spacemit: support the SpacemiT P1 RTC

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Message-ID: <20250723213956570da462@mail.local>
Date: Wed, 23 Jul 2025 23:39:56 +0200
From: Alexandre Belloni <alexandre.belloni@...tlin.com>
To: Alex Elder <elder@...cstar.com>
Cc: lee@...nel.org, lgirdwood@...il.com, broonie@...nel.org,
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	mat.jonczyk@...pl, dlan@...too.org, paul.walmsley@...ive.com,
	palmer@...belt.com, aou@...s.berkeley.edu, alex@...ti.fr,
	troymitchell988@...il.com, guodong@...cstar.com,
	linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
	linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 5/8] rtc: spacemit: support the SpacemiT P1 RTC

On 10/07/2025 12:51:03-0500, Alex Elder wrote:
> +static int p1_rtc_read_time(struct device *dev, struct rtc_time *t)
> +{
> +	struct p1_rtc *p1 = dev_get_drvdata(dev);
> +	struct regmap *regmap = p1->regmap;
> +	u32 count = RTC_READ_TRIES;
> +	u8 seconds;
> +	u8 time[6];
> +	int ret;
> +
> +	if (!regmap_test_bits(regmap, RTC_CTRL, RTC_EN))
> +		return -ENODEV;		/* RTC is disabled */

That should be -EINVAL, as all the other drivers have standardized this.

With this fixed,
Acked-by: Alexandre Belloni <alexandre.belloni@...tlin.com>


> +
> +	ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
> +	if (ret)
> +		return ret;
> +
> +	do {
> +		seconds = time[0];
> +		ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
> +		if (ret)
> +			return ret;
> +	} while (time[0] != seconds && --count);
> +
> +	if (!count)
> +		return -EIO;		/* Unable to get a consistent result */
> +
> +	t->tm_sec = time[0] & GENMASK(5, 0);
> +	t->tm_min = time[1] & GENMASK(5, 0);
> +	t->tm_hour = time[2] & GENMASK(4, 0);
> +	t->tm_mday = (time[3] & GENMASK(4, 0)) + 1;
> +	t->tm_mon = time[4] & GENMASK(3, 0);
> +	t->tm_year = (time[5] & GENMASK(5, 0)) + 100;
> +
> +	return 0;
> +}
> +
> +/*
> + * The P1 hardware documentation states that values in the registers are
> + * latched so when written they represent a consistent time snapshot.
> + * Nevertheless, this is not guaranteed by the implementation, so we must
> + * disable the RTC while updating it.
> + */
> +static int p1_rtc_set_time(struct device *dev, struct rtc_time *t)
> +{
> +	struct p1_rtc *p1 = dev_get_drvdata(dev);
> +	struct regmap *regmap = p1->regmap;
> +	u8 time[6];
> +	int ret;
> +
> +	time[0] = t->tm_sec;
> +	time[1] = t->tm_min;
> +	time[2] = t->tm_hour;
> +	time[3] = t->tm_mday - 1;
> +	time[4] = t->tm_mon;
> +	time[5] = t->tm_year - 100;
> +
> +	/* Disable the RTC to update; re-enable again when done */
> +	ret = regmap_clear_bits(regmap, RTC_CTRL, RTC_EN);
> +	if (ret)
> +		return ret;
> +
> +	/* If something goes wrong, leave the RTC disabled */
> +	ret = regmap_bulk_write(regmap, RTC_TIME, time, sizeof(time));
> +	if (ret)
> +		return ret;
> +
> +	return regmap_set_bits(regmap, RTC_CTRL, RTC_EN);
> +}
> +
> +static const struct rtc_class_ops p1_rtc_class_ops = {
> +	.read_time = p1_rtc_read_time,
> +	.set_time = p1_rtc_set_time,
> +};
> +
> +static int p1_rtc_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct rtc_device *rtc;
> +	struct p1_rtc *p1;
> +
> +	p1 = devm_kzalloc(dev, sizeof(*p1), GFP_KERNEL);
> +	if (!p1)
> +		return -ENOMEM;
> +	dev_set_drvdata(dev, p1);
> +
> +	p1->regmap = dev_get_regmap(dev->parent, NULL);
> +	if (!p1->regmap)
> +		return dev_err_probe(dev, -ENODEV, "failed to get regmap\n");
> +
> +	rtc = devm_rtc_allocate_device(dev);
> +	if (IS_ERR(rtc))
> +		return dev_err_probe(dev, PTR_ERR(rtc),
> +				     "error allocating device\n");
> +	p1->rtc = rtc;
> +
> +	rtc->ops = &p1_rtc_class_ops;
> +	rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
> +	rtc->range_max = RTC_TIMESTAMP_END_2063;
> +
> +	clear_bit(RTC_FEATURE_ALARM, rtc->features);
> +	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
> +
> +	return devm_rtc_register_device(rtc);
> +}
> +
> +static struct platform_driver p1_rtc_driver = {
> +	.probe = p1_rtc_probe,
> +	.driver = {
> +		.name = MOD_NAME,
> +	},
> +};
> +
> +module_platform_driver(p1_rtc_driver);
> +
> +MODULE_DESCRIPTION("SpacemiT P1 RTC driver");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:" MOD_NAME);
> -- 
> 2.45.2
> 

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