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Message-ID: <20251115112421bdd368f5@mail.local>
Date: Sat, 15 Nov 2025 12:24:21 +0100
From: Alexandre Belloni <alexandre.belloni@...tlin.com>
To: Akhilesh Patil <akhilesh@...iitb.ac.in>
Cc: andriy.shevchenko@...el.com, david.daney@...ium.com,
ddaney@...iumnetworks.com, david.hunter.linux@...il.com,
skhan@...uxfoundation.org, linux-rtc@...r.kernel.org,
linux-kernel@...r.kernel.org, akhileshpatilvnit@...il.com
Subject: Re: [PATCH] rtc: isl12026: Implement callbacks for alarm feature
On 15/11/2025 16:35:06+0530, Akhilesh Patil wrote:
> Add alarm support for isl12026 RTC. Implement alarm function rtc
> class callbacks - set_alarm, read_alarm and alarm_irq_enable.
> isl12026 rtc has 2 alarms, this patch adds support to configure alarm0.
> Note: isl12026 rtc chip share same pin(4) for alarm interrupt and square
> wave frequency generator, hence forcefully disable SQW functionality
> while writing to device registers in alarm functions.
>
> Tested on TI am62x sk board on i2c-2 port using selftests/rtc/rtctest
>
> Signed-off-by: Akhilesh Patil <akhilesh@...iitb.ac.in>
> ---
> Datasheet of RTC chip.
> https://www.renesas.com/en/document/dst/isl12026-isl12026a-datasheet?srsltid=AfmBOopgN4vtn8XoN-8sOCfTW6yiLH-T7eeH_IWakqZ2VmENmWFqqh7w
>
> drivers/rtc/rtc-isl12026.c | 127 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 127 insertions(+)
>
> diff --git a/drivers/rtc/rtc-isl12026.c b/drivers/rtc/rtc-isl12026.c
> index 2aabb9151d4c..7fa9ec7e4929 100644
> --- a/drivers/rtc/rtc-isl12026.c
> +++ b/drivers/rtc/rtc-isl12026.c
> @@ -34,6 +34,11 @@
> #define ISL12026_PAGESIZE 16
> #define ISL12026_NVMEM_WRITE_TIME 20
>
> +#define ISL12026_AL0_REG_SC 0x0
> +#define ISL12026_REG_INT 0x11
> +#define ISL12026_AL0E BIT(5)
> +#define ISL12026_SR_AL0 BIT(5)
> +
> struct isl12026 {
> struct rtc_device *rtc;
> struct i2c_client *nvm_client;
> @@ -269,9 +274,131 @@ static int isl12026_rtc_read_time(struct device *dev, struct rtc_time *tm)
> return ret;
> }
>
> +static int isl12026_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> +{
> + struct i2c_client *client = to_i2c_client(dev);
> + int ret;
> + u8 buf_alrm_vals[7];
> + struct i2c_msg msg;
> + int ir;
> +
> + msg.addr = client->addr;
> + msg.flags = 0x0; /* Write operation */
> + msg.buf = buf_alrm_vals;
> + msg.len = sizeof(buf_alrm_vals);
> +
> + if (!alrm->enabled) {
> + /* Disable alarm and return */
You still need to set the alarm time and date properly, the application
is allowed to first set the alarm and then enable it.
> + ir = isl12026_read_reg(client, ISL12026_REG_INT);
> + if (ir < 0)
> + return ir;
> + ir &= ~ISL12026_AL0E;
> + ret = isl12026_write_reg(client, ISL12026_REG_INT, ir);
> +
> + return ret;
> + }
> +
> + /* Prepare 5 bytes alarm data SC, MN, HR, DT, MO */
> + buf_alrm_vals[0] = 0x0;
> + buf_alrm_vals[1] = ISL12026_AL0_REG_SC;
> + buf_alrm_vals[2] = (bin2bcd(alrm->time.tm_sec) & 0x7f) | 0x80;
> + buf_alrm_vals[3] = (bin2bcd(alrm->time.tm_min) & 0x7f) | 0x80;
> + buf_alrm_vals[4] = (bin2bcd(alrm->time.tm_hour) & 0x3f) | 0x80;
> + buf_alrm_vals[5] = (bin2bcd(alrm->time.tm_mday) & 0x3f) | 0x80;
> + buf_alrm_vals[6] = (bin2bcd(alrm->time.tm_mon + 1) & 0x1f) | 0x80;
> +
> + /* Non-volatile Page write to AL0 registers and enable INT */
> + ret = isl12026_arm_write(client);
> + if (ret < 0)
> + return ret;
> + ret = i2c_transfer(client->adapter, &msg, 1);
> + msleep(ISL12026_NVMEM_WRITE_TIME);
> + if (ret != 1) {
> + dev_err(&client->dev, "Error writing to alarm registers\n");
No need for an error message.
> + return ret < 0 ? ret : -EIO;
> + }
> +
> + /* Enable AL0 interrupt */
> + ret = isl12026_write_reg(client, ISL12026_REG_INT, ISL12026_AL0E);
> +
> + return ret;
> +}
> +
> +static int isl12026_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
> +{
> + struct i2c_client *client = to_i2c_client(dev);
> + int ret;
> + int sr, ir;
> + u8 buf_alrm_vals[5];
> + u8 addr[2] = {0x0, ISL12026_AL0_REG_SC};
> + struct i2c_msg msgs[2] = { };
> +
> + msgs[0].addr = client->addr;
> + msgs[0].flags = 0x0; /* Write register address */
> + msgs[0].buf = addr;
> + msgs[0].len = sizeof(addr);
> +
> + msgs[1].addr = client->addr;
> + msgs[1].flags = I2C_M_RD; /* Alarm read operation */
> + msgs[1].buf = buf_alrm_vals;
> + msgs[1].len = sizeof(buf_alrm_vals);
> +
> + /* Read alarm enable status */
> + ir = isl12026_read_reg(client, ISL12026_REG_INT);
> + if (ir < 0)
> + return ir;
> + alrm->enabled = !!(ir & ISL12026_AL0E);
> +
> + /* Read alarm pending status */
> + sr = isl12026_read_reg(client, ISL12026_REG_SR);
> + if (sr < 0)
> + return sr;
> + alrm->pending = !!(sr & ISL12026_SR_AL0) && alrm->enabled;
> +
> + /* Page read for alarm registers */
> + ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
> + if (ret != ARRAY_SIZE(msgs)) {
> + dev_err(&client->dev, "Error reading alarm registers\n");
Ditto
> + return ret < 0 ? ret : -EIO;
> + }
> +
> + /* Populate values read */
> + alrm->time.tm_sec = bcd2bin(buf_alrm_vals[0] & 0x7f);
> + alrm->time.tm_min = bcd2bin(buf_alrm_vals[1] & 0x7f);
> + alrm->time.tm_hour = bcd2bin(buf_alrm_vals[2] & 0x3f);
> + alrm->time.tm_mday = bcd2bin(buf_alrm_vals[3] & 0x3f);
> + alrm->time.tm_mon = bcd2bin(buf_alrm_vals[4] & 0x1f) - 1;
> +
> + return 0;
> +}
> +
> +static int isl12026_rtc_alarm_irq_en(struct device *dev, unsigned int enabled)
> +{
> + struct i2c_client *client = to_i2c_client(dev);
> + int ret;
> + int ir;
> +
> + if (enabled) {
> + ret = isl12026_write_reg(client, ISL12026_REG_INT, ISL12026_AL0E);
> + return ret;
> + }
> +
> + /* Disable alarm */
> + ir = isl12026_read_reg(client, ISL12026_REG_INT);
> + if (ir < 0)
> + return ir;
> + ir &= ~ISL12026_AL0E;
> + ret = isl12026_write_reg(client, ISL12026_REG_INT, ir);
> +
> + return ret;
> +}
> +
> static const struct rtc_class_ops isl12026_rtc_ops = {
> .read_time = isl12026_rtc_read_time,
> .set_time = isl12026_rtc_set_time,
> + .set_alarm = isl12026_rtc_set_alarm,
> + .read_alarm = isl12026_rtc_read_alarm,
> + .alarm_irq_enable = isl12026_rtc_alarm_irq_en,
> };
>
This is missing an interrupt handler and proper handling in probe for
the wakeup-source property as this seems to be how you use it.
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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