[PATCH v3 4/7] rtc: spacemit: support the SpacemiT P1 RTC

Alex Elder elder at riscstar.com
Mon Jun 23 13:03:25 PDT 2025


On 6/23/25 2:14 PM, Alexandre Belloni wrote:
> Hello,
> 
> On 21/06/2025 22:29:36-0500, Alex Elder wrote:
>> Add support for the RTC found in the SpacemiT P1 PMIC.  Initially
>> only setting and reading the time are supported.
>>
>> The PMIC is implemented as a multi-function device.  This RTC is
>> probed based on this driver being named in a MFD cell in the simple
>> MFD I2C driver.
>>
>> Signed-off-by: Alex Elder <elder at riscstar.com>
>> ---
>> v3: - Added this driver to the series, in response to Lee Jones saying
>>        more than one MFD sub-device was required to be acceptable
>>
>>   drivers/rtc/Kconfig  |  10 ++++
>>   drivers/rtc/Makefile |   1 +
>>   drivers/rtc/rtc-p1.c | 137 +++++++++++++++++++++++++++++++++++++++++++
> 
> We need something more descriptive than p1 here

Are you referring to the chip itself, or do you want a longer
file name?   Do you prefer "rtc-spacemit-p1.c" or something?

>>   3 files changed, 148 insertions(+)
>>   create mode 100644 drivers/rtc/rtc-p1.c
>>
>> diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
>> index 9aec922613cec..27cff02ba4e66 100644
>> --- a/drivers/rtc/Kconfig
>> +++ b/drivers/rtc/Kconfig
>> @@ -406,6 +406,16 @@ config RTC_DRV_MAX77686
>>   	  This driver can also be built as a module. If so, the module
>>   	  will be called rtc-max77686.
>>   
>> +config RTC_DRV_P1
> 
> Ditto
> 
>> +	tristate "SpacemiT P1 RTC"
>> +	depends on ARCH_SPACEMIT || COMPILE_TEST
>> +	select MFD_SPACEMIT_P1
>> +	default ARCH_SPACEMIT
>> +	help
>> +	  Enable support for the RTC function in the SpacemiT P1 PMIC.
>> +	  This driver can also be built as a module, which will be called
>> +	  "spacemit-p1-rtc".
>> +
>>   config RTC_DRV_NCT3018Y
>>   	tristate "Nuvoton NCT3018Y"
>>   	depends on OF
>> diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
>> index 4619aa2ac4697..f8588426e2ba4 100644
>> --- a/drivers/rtc/Makefile
>> +++ b/drivers/rtc/Makefile
>> @@ -171,6 +171,7 @@ obj-$(CONFIG_RTC_DRV_SD2405AL)	+= rtc-sd2405al.o
>>   obj-$(CONFIG_RTC_DRV_SD3078)	+= rtc-sd3078.o
>>   obj-$(CONFIG_RTC_DRV_SH)	+= rtc-sh.o
>>   obj-$(CONFIG_RTC_DRV_SNVS)	+= rtc-snvs.o
>> +obj-$(CONFIG_RTC_DRV_P1)	+= rtc-p1.o
>>   obj-$(CONFIG_RTC_DRV_SPEAR)	+= rtc-spear.o
>>   obj-$(CONFIG_RTC_DRV_STARFIRE)	+= rtc-starfire.o
>>   obj-$(CONFIG_RTC_DRV_STK17TA8)	+= rtc-stk17ta8.o
>> diff --git a/drivers/rtc/rtc-p1.c b/drivers/rtc/rtc-p1.c
>> new file mode 100644
>> index 0000000000000..e0d2c0c822142
>> --- /dev/null
>> +++ b/drivers/rtc/rtc-p1.c
>> @@ -0,0 +1,137 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Driver for the RTC found in the SpacemiT P1 PMIC
>> + *
>> + * Copyright (C) 2025 by RISCstar Solutions Corporation.  All rights reserved.
>> + */
>> +
>> +#include <linux/bits.h>
>> +#include <linux/device.h>
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/regmap.h>
>> +#include <linux/rtc.h>
>> +
>> +#define MOD_NAME	"spacemit-p1-rtc"
>> +
>> +/* Offset to byte containing the given time unit */
>> +enum time_unit {
>> +	tu_second = 0,		/* 0-59 */
>> +	tu_minute,		/* 0-59 */
>> +	tu_hour,		/* 0-59 */
>> +	tu_day,			/* 0-30 (struct tm uses 1-31) */
>> +	tu_month,		/* 0-11 */
>> +	tu_year,		/* Years since 2000 (struct tm uses 1900) */
>> +	tu_count,		/* Last; not a time unit */
>> +};
> 
> I'm not sure this enum actually brings anything

It's just defining the sequence of register values
symbolically.  Do you prefer #defines?

It doesn't matter much to me, I just want to know what
you'd prefer.

> 
>> +
>> +/* Consecutive bytes contain seconds, minutes, etc. */
>> +#define RTC_COUNT_BASE		0x0d
>> +
>> +#define RTC_CTRL		0x1d
>> +#define RTC_EN		BIT(2)
>> +
>> +struct p1_rtc {
>> +	struct regmap *regmap;
>> +	struct rtc_device *rtc;
>> +};
>> +
>> +static int p1_rtc_read_time(struct device *dev, struct rtc_time *t)
>> +{
>> +	struct p1_rtc *p1 = dev_get_drvdata(dev);
>> +	u8 time[tu_count];
>> +	int ret;
>> +
>> +	ret = regmap_bulk_read(p1->regmap, RTC_COUNT_BASE, &time, sizeof(time));
>> +	if (ret)
>> +		return ret;
>> +
>> +	t->tm_sec = time[tu_second] & GENMASK(5, 0);
>> +	t->tm_min = time[tu_minute] & GENMASK(5, 0);
>> +	t->tm_hour = time[tu_hour] & GENMASK(4, 0);
>> +	t->tm_mday = (time[tu_day] & GENMASK(4, 0)) + 1;
>> +	t->tm_mon = time[tu_month] & GENMASK(3, 0);
>> +	t->tm_year = (time[tu_year] & GENMASK(5, 0)) + 100;
>> +	/* tm_wday, tm_yday, and tm_isdst aren't used */
>> +
>> +	return 0;
>> +}
>> +
>> +static int p1_rtc_set_time(struct device *dev, struct rtc_time *t)
>> +{
>> +	struct p1_rtc *p1 = dev_get_drvdata(dev);
>> +	u8 time[tu_count];
>> +	int ret;
>> +
>> +	time[tu_second] = t->tm_sec;
>> +	time[tu_minute] = t->tm_min;
>> +	time[tu_hour] = t->tm_hour;
>> +	time[tu_day] = t->tm_mday - 1;
>> +	time[tu_month] = t->tm_mon;
>> +	time[tu_year] = t->tm_year - 100;
>> +
>> +	/* Disable the RTC to update; re-enable again when done */
>> +	ret = regmap_update_bits(p1->regmap, RTC_CTRL, RTC_EN, 0);
>> +	if (ret)
>> +		return ret;
>> +
>> +	ret = regmap_bulk_write(p1->regmap, RTC_COUNT_BASE, time, sizeof(time));
>> +
>> +	(void)regmap_update_bits(p1->regmap, RTC_CTRL, RTC_EN, RTC_EN);
> 
> Don't you care whether the RTC has been reenabled?

Yes, Mateusz pointed this out.  I'll fix this.

I hope that disabling and re-enabling isn't require,
which makes the error possibilities a lot simpler.

Otherwise it's not clear how best to recover from
an error re-enabling the RTC (but yes, if no error
occurs in the bulk write, an error when re-enabling
will be returned).

>> +
>> +	return ret;
>> +}
>> +
>> +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;
>> +	int ret;
>> +
>> +	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);
>> +
>> +	ret = devm_rtc_register_device(rtc);
>> +	if (ret)
>> +		return dev_err_probe(dev, ret, "error registering RTC\n");
> 
> This message is unnecessary, there are no silent error path in
> devm_rtc_register_device

Awesome.  I'll just return what devm_rtc_regsister_device()
returns.

Thanks a lot.

					-Alex

> 
>> +
>> +	return 0;
>> +}
>> +
>> +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);
> 




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