Implement alarm feature for rtc-m41t93 by adding necessary
callbacks - set_alarm, read_alarm and alarm_irq_enable.
Enable support to configure alarm 1 out of 2 alarms present in this rtc.

Tested by observing IRQ pin (pin 12 of SOX18 package) on logic analyzer
going low after alarm condition is met.

Signed-off-by: Akhilesh Patil <akhilesh@ee.iitb.ac.in>
---
 drivers/rtc/rtc-m41t93.c | 101 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)

diff --git a/drivers/rtc/rtc-m41t93.c b/drivers/rtc/rtc-m41t93.c
index ad862bf706b6..8cc179e08a4a 100644
--- a/drivers/rtc/rtc-m41t93.c
+++ b/drivers/rtc/rtc-m41t93.c
@@ -22,6 +22,14 @@
 #define M41T93_REG_DAY			5
 #define M41T93_REG_MON			6
 #define M41T93_REG_YEAR			7
+#define M41T93_REG_AL1_MONTH		0xa
+#define M41T93_REG_AL1_DATE		0xb
+#define M41T93_REG_AL1_HOUR		0xc
+#define M41T93_REG_AL1_MIN		0xd
+#define M41T93_REG_AL1_SEC		0xe
+#define M41T93_BIT_A1IE                 BIT(7)
+#define M41T93_BIT_ABE			BIT(5)
+#define M41T93_FLAG_AF1                 BIT(6)
 
 
 #define M41T93_REG_ALM_HOUR_HT		0xc
@@ -153,10 +161,103 @@ static int m41t93_get_time(struct device *dev, struct rtc_time *tm)
 	return ret;
 }
 
+static int m41t93_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct m41t93_data *m41t93 = dev_get_drvdata(dev);
+	int ret;
+	unsigned int val;
+	u8 alarm_vals[5] = {0};
+
+	ret = regmap_bulk_write(m41t93->regmap, M41T93_REG_AL1_DATE, alarm_vals, 4);
+	if (ret)
+		return ret;
+
+	/* Set alarm values */
+	alarm_vals[0] = bin2bcd(alrm->time.tm_mon + 1) & 0x1f;
+	alarm_vals[1] = bin2bcd(alrm->time.tm_mday) & 0x3f;
+	alarm_vals[2] = bin2bcd(alrm->time.tm_hour) & 0x3f;
+	alarm_vals[3] = bin2bcd(alrm->time.tm_min) & 0x7f;
+	alarm_vals[4] = bin2bcd(alrm->time.tm_sec) & 0x7f;
+
+	if (alrm->enabled) {
+		/* Enable alarm IRQ generation
+		 * Note: SQWE is forced disabled while setting alarm
+		 */
+		alarm_vals[0] |= M41T93_BIT_A1IE | M41T93_BIT_ABE;
+	}
+
+	ret = regmap_bulk_write(m41t93->regmap, M41T93_REG_AL1_MONTH,
+				alarm_vals, sizeof(alarm_vals));
+	if (ret)
+		return ret;
+
+	/* Device address pointer is now at FLAG register, move it to other location
+	 * to finish setting alarm, as recommended by the datasheet.
+	 * We do read of AL1_MONTH register to achieve this.
+	 */
+	ret = regmap_read(m41t93->regmap, M41T93_REG_AL1_MONTH, &val);
+	if (ret)
+		return ret;
+
+	if (bcd2bin(val & 0x1f) == (alrm->time.tm_mon & 0x1f))
+		dev_notice(dev, "Alarm set successfully\n");
+
+	return 0;
+}
+
+static int m41t93_get_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct m41t93_data *m41t93 = dev_get_drvdata(dev);
+	int ret;
+	unsigned int val;
+	u8 alarm_vals[5] = {0};
+
+	ret = regmap_bulk_read(m41t93->regmap, M41T93_REG_AL1_MONTH,
+			       alarm_vals, sizeof(alarm_vals));
+	if (ret)
+		return ret;
+
+	alrm->time.tm_mon = bcd2bin(alarm_vals[0] & 0x1f) - 1;
+	alrm->time.tm_mday = bcd2bin(alarm_vals[1] & 0x3f);
+	alrm->time.tm_hour = bcd2bin(alarm_vals[2] & 0x3f);
+	alrm->time.tm_min = bcd2bin(alarm_vals[3] & 0x7f);
+	alrm->time.tm_sec = bcd2bin(alarm_vals[4] & 0x7f);
+
+	alrm->enabled =  !!(alarm_vals[0] & M41T93_BIT_A1IE);
+
+	ret = regmap_read(m41t93->regmap, M41T93_REG_FLAGS, &val);
+	if (ret)
+		return ret;
+
+	alrm->pending = (val & M41T93_FLAG_AF1) && alrm->enabled;
+
+	return 0;
+}
+
+static int m41t93_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct m41t93_data *m41t93 = dev_get_drvdata(dev);
+	unsigned int val;
+	int ret;
+
+	val = enabled ? M41T93_BIT_A1IE | M41T93_BIT_ABE :
+		~(M41T93_BIT_A1IE | M41T93_BIT_ABE);
+
+	ret = regmap_update_bits(m41t93->regmap, M41T93_REG_AL1_MONTH,
+				 M41T93_BIT_A1IE | M41T93_BIT_ABE, val);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
 
 static const struct rtc_class_ops m41t93_rtc_ops = {
 	.read_time	= m41t93_get_time,
 	.set_time	= m41t93_set_time,
+	.set_alarm	= m41t93_set_alarm,
+	.read_alarm	= m41t93_get_alarm,
+	.alarm_irq_enable = m41t93_alarm_irq_enable,
 };
 
 static struct spi_driver m41t93_driver;
-- 
2.34.1

Hi Akhilesh,

kernel test robot noticed the following build warnings:

[auto build test WARNING on abelloni/rtc-next]
[also build test WARNING on linus/master v6.17-rc4 next-20250903]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Akhilesh-Patil/rtc-m41t93-add-device-tree-support/20250903-223155
base:   https://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux.git rtc-next
patch link:    https://lore.kernel.org/r/4f78f8fa113d4262e162972f5c15155410a64e8b.1756908788.git.akhilesh%40ee.iitb.ac.in
patch subject: [PATCH 4/7] rtc: m41t93: Add alarm support
config: loongarch-randconfig-002-20250904 (https://download.01.org/0day-ci/archive/20250904/202509041246.7GqISV63-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 2e122990391b2ba062e6308a12cfedf7206270ba)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250904/202509041246.7GqISV63-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509041246.7GqISV63-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/rtc/rtc-m41t93.c:244:3: warning: implicit conversion from 'unsigned long' to 'unsigned int' changes value from 18446744073709551455 to 4294967135 [-Wconstant-conversion]
     243 |         val = enabled ? M41T93_BIT_A1IE | M41T93_BIT_ABE :
         |             ~
     244 |                 ~(M41T93_BIT_A1IE | M41T93_BIT_ABE);
         |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   1 warning generated.


vim +244 drivers/rtc/rtc-m41t93.c

   236	
   237	static int m41t93_alarm_irq_enable(struct device *dev, unsigned int enabled)
   238	{
   239		struct m41t93_data *m41t93 = dev_get_drvdata(dev);
   240		unsigned int val;
   241		int ret;
   242	
   243		val = enabled ? M41T93_BIT_A1IE | M41T93_BIT_ABE :
 > 244			~(M41T93_BIT_A1IE | M41T93_BIT_ABE);
   245	
   246		ret = regmap_update_bits(m41t93->regmap, M41T93_REG_AL1_MONTH,
   247					 M41T93_BIT_A1IE | M41T93_BIT_ABE, val);
   248		if (ret)
   249			return ret;
   250	
   251		return 0;
   252	}
   253	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki