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Message-ID: <20211130095004.22777-1-camel.guo@axis.com>
Date: Tue, 30 Nov 2021 10:50:04 +0100
From: Camel Guo <camel.guo@...s.com>
To: Alessandro Zummo <a.zummo@...ertech.it>,
Alexandre Belloni <alexandre.belloni@...tlin.com>
CC: <kernel@...s.com>, Camel Guo <camelg@...s.com>,
<linux-rtc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] rtc: rs5c372: add offset correction support
From: Camel Guo <camelg@...s.com>
This commit adds support of offset correction by configuring the
oscillation adjustment register of rs5c372.
Signed-off-by: Camel Guo <camelg@...s.com>
---
drivers/rtc/rtc-rs5c372.c | 80 +++++++++++++++++++++++++++++++++++++++
1 file changed, 80 insertions(+)
diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
index 80980414890c..77027498cad5 100644
--- a/drivers/rtc/rtc-rs5c372.c
+++ b/drivers/rtc/rtc-rs5c372.c
@@ -30,6 +30,8 @@
#define RS5C372_REG_TRIM 7
# define RS5C372_TRIM_XSL 0x80
# define RS5C372_TRIM_MASK 0x7F
+# define RS5C372_TRIM_DEV (1 << 7)
+# define RS5C372_TRIM_DECR (1 << 6)
#define RS5C_REG_ALARM_A_MIN 8 /* or ALARM_W */
#define RS5C_REG_ALARM_A_HOURS 9
@@ -485,6 +487,82 @@ static int rs5c372_rtc_proc(struct device *dev, struct seq_file *seq)
#define rs5c372_rtc_proc NULL
#endif
+static int rs5c372_read_offset(struct device *dev, long *offset)
+{
+ struct rs5c372 *rs5c = i2c_get_clientdata(to_i2c_client(dev));
+ int addr = RS5C_ADDR(RS5C372_REG_TRIM);
+ unsigned char val = i2c_smbus_read_byte_data(rs5c->client, addr);
+ long ppb_per_step = (val & RS5C372_TRIM_DEV) ? 1017 : 3052;
+ unsigned char decr = val & RS5C372_TRIM_DECR;
+
+ /* Only bits[0:5] repsents the time counts */
+ val &= 0x3F;
+
+ /* If bits[1:5] are all 0, it means no increment or decrement */
+ if (!(val & 0x3E)) {
+ *offset = 0;
+ } else {
+ if (decr)
+ *offset = -(((~val) & 0x3F) + 1) * ppb_per_step;
+ else
+ *offset = (val - 1) * ppb_per_step;
+ }
+
+ return 0;
+}
+
+static int rs5c372_set_offset(struct device *dev, long offset)
+{
+ struct rs5c372 *rs5c = i2c_get_clientdata(to_i2c_client(dev));
+ int addr = RS5C_ADDR(RS5C372_REG_TRIM);
+ unsigned char val = RS5C372_TRIM_DEV;
+ long steps = 0;
+
+ /*
+ * Check if it is possible to use high resolution mode (DEV=1). In this
+ * mode, the minimum resolution is 2 / (32768 * 20 * 3), which is about
+ * 1017 ppb
+ */
+ steps = DIV_ROUND_CLOSEST(offset, 1017);
+ if (steps > 0x3E || steps < -0x3E) {
+ /*
+ * offset is out of the range of high resolution mode. Try to
+ * use low resolution mode (DEV=0). In this mode, the minimum
+ * resolution is 2 / (32768 * 20), which is about 3052 ppb.
+ */
+ val &= ~RS5C372_TRIM_DEV;
+ steps = DIV_ROUND_CLOSEST(offset, 3052);
+
+ if (steps > 0x3E || steps < -0x3E)
+ return -ERANGE;
+ }
+
+ if (steps > 0) {
+ val |= steps + 1;
+ } else {
+ val |= RS5C372_TRIM_DECR;
+ val |= (~(-steps - 1)) & 0x3F;
+ }
+
+ if (!steps || !(val & 0x3E)) {
+ /*
+ * if offset is too small, set oscillation adjustment register
+ * with the default values, which means no increment or
+ * decrement.
+ */
+ val = 0;
+ }
+
+ dev_dbg(&rs5c->client->dev, "write 0x%x for offset %ld\n", val, offset);
+
+ if (i2c_smbus_write_byte_data(rs5c->client, addr, val) < 0) {
+ dev_err(&rs5c->client->dev, "failed to write 0x%x to reg %d\n", val, addr);
+ return -EIO;
+ }
+
+ return 0;
+}
+
static const struct rtc_class_ops rs5c372_rtc_ops = {
.proc = rs5c372_rtc_proc,
.read_time = rs5c372_rtc_read_time,
@@ -492,6 +570,8 @@ static const struct rtc_class_ops rs5c372_rtc_ops = {
.read_alarm = rs5c_read_alarm,
.set_alarm = rs5c_set_alarm,
.alarm_irq_enable = rs5c_rtc_alarm_irq_enable,
+ .read_offset = rs5c372_read_offset,
+ .set_offset = rs5c372_set_offset,
};
#if IS_ENABLED(CONFIG_RTC_INTF_SYSFS)
--
2.20.1
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