144 lines
4.5 KiB
Diff
144 lines
4.5 KiB
Diff
commit f94ffbc2c2a4128c4412bb483d0807722dfb682b
|
|
Author: Russell King <rmk+kernel@armlinux.org.uk>
|
|
Date: Fri Sep 29 11:23:31 2017 +0100
|
|
|
|
rtc: armada38x: add support for trimming the RTC
|
|
|
|
Add support for trimming the RTC using the offset mechanism. This RTC
|
|
supports two modes: low update mode and high update mode. Low update
|
|
mode has finer precision than high update mode, so we use the low mode
|
|
where possible.
|
|
|
|
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
|
|
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
|
|
|
|
--- a/drivers/rtc/rtc-armada38x.c
|
|
+++ b/drivers/rtc/rtc-armada38x.c
|
|
@@ -28,6 +28,8 @@
|
|
#define RTC_IRQ_AL_EN BIT(0)
|
|
#define RTC_IRQ_FREQ_EN BIT(1)
|
|
#define RTC_IRQ_FREQ_1HZ BIT(2)
|
|
+#define RTC_CCR 0x18
|
|
+#define RTC_CCR_MODE BIT(15)
|
|
|
|
#define RTC_TIME 0xC
|
|
#define RTC_ALARM1 0x10
|
|
@@ -343,18 +345,117 @@ static irqreturn_t armada38x_rtc_alarm_i
|
|
return IRQ_HANDLED;
|
|
}
|
|
|
|
+/*
|
|
+ * The information given in the Armada 388 functional spec is complex.
|
|
+ * They give two different formulas for calculating the offset value,
|
|
+ * but when considering "Offset" as an 8-bit signed integer, they both
|
|
+ * reduce down to (we shall rename "Offset" as "val" here):
|
|
+ *
|
|
+ * val = (f_ideal / f_measured - 1) / resolution where f_ideal = 32768
|
|
+ *
|
|
+ * Converting to time, f = 1/t:
|
|
+ * val = (t_measured / t_ideal - 1) / resolution where t_ideal = 1/32768
|
|
+ *
|
|
+ * => t_measured / t_ideal = val * resolution + 1
|
|
+ *
|
|
+ * "offset" in the RTC interface is defined as:
|
|
+ * t = t0 * (1 + offset * 1e-9)
|
|
+ * where t is the desired period, t0 is the measured period with a zero
|
|
+ * offset, which is t_measured above. With t0 = t_measured and t = t_ideal,
|
|
+ * offset = (t_ideal / t_measured - 1) / 1e-9
|
|
+ *
|
|
+ * => t_ideal / t_measured = offset * 1e-9 + 1
|
|
+ *
|
|
+ * so:
|
|
+ *
|
|
+ * offset * 1e-9 + 1 = 1 / (val * resolution + 1)
|
|
+ *
|
|
+ * We want "resolution" to be an integer, so resolution = R * 1e-9, giving
|
|
+ * offset = 1e18 / (val * R + 1e9) - 1e9
|
|
+ * val = (1e18 / (offset + 1e9) - 1e9) / R
|
|
+ * with a common transformation:
|
|
+ * f(x) = 1e18 / (x + 1e9) - 1e9
|
|
+ * offset = f(val * R)
|
|
+ * val = f(offset) / R
|
|
+ *
|
|
+ * Armada 38x supports two modes, fine mode (954ppb) and coarse mode (3815ppb).
|
|
+ */
|
|
+static long armada38x_ppb_convert(long ppb)
|
|
+{
|
|
+ long div = ppb + 1000000000L;
|
|
+
|
|
+ return div_s64(1000000000000000000LL + div / 2, div) - 1000000000L;
|
|
+}
|
|
+
|
|
+static int armada38x_rtc_read_offset(struct device *dev, long *offset)
|
|
+{
|
|
+ struct armada38x_rtc *rtc = dev_get_drvdata(dev);
|
|
+ unsigned long ccr, flags;
|
|
+ long ppb_cor;
|
|
+
|
|
+ spin_lock_irqsave(&rtc->lock, flags);
|
|
+ ccr = rtc->data->read_rtc_reg(rtc, RTC_CCR);
|
|
+ spin_unlock_irqrestore(&rtc->lock, flags);
|
|
+
|
|
+ ppb_cor = (ccr & RTC_CCR_MODE ? 3815 : 954) * (s8)ccr;
|
|
+ /* ppb_cor + 1000000000L can never be zero */
|
|
+ *offset = armada38x_ppb_convert(ppb_cor);
|
|
+
|
|
+ return 0;
|
|
+}
|
|
+
|
|
+static int armada38x_rtc_set_offset(struct device *dev, long offset)
|
|
+{
|
|
+ struct armada38x_rtc *rtc = dev_get_drvdata(dev);
|
|
+ unsigned long ccr = 0;
|
|
+ long ppb_cor, off;
|
|
+
|
|
+ /*
|
|
+ * The maximum ppb_cor is -128 * 3815 .. 127 * 3815, but we
|
|
+ * need to clamp the input. This equates to -484270 .. 488558.
|
|
+ * Not only is this to stop out of range "off" but also to
|
|
+ * avoid the division by zero in armada38x_ppb_convert().
|
|
+ */
|
|
+ offset = clamp(offset, -484270L, 488558L);
|
|
+
|
|
+ ppb_cor = armada38x_ppb_convert(offset);
|
|
+
|
|
+ /*
|
|
+ * Use low update mode where possible, which gives a better
|
|
+ * resolution of correction.
|
|
+ */
|
|
+ off = DIV_ROUND_CLOSEST(ppb_cor, 954);
|
|
+ if (off > 127 || off < -128) {
|
|
+ ccr = RTC_CCR_MODE;
|
|
+ off = DIV_ROUND_CLOSEST(ppb_cor, 3815);
|
|
+ }
|
|
+
|
|
+ /*
|
|
+ * Armada 388 requires a bit pattern in bits 14..8 depending on
|
|
+ * the sign bit: { 0, ~S, S, S, S, S, S }
|
|
+ */
|
|
+ ccr |= (off & 0x3fff) ^ 0x2000;
|
|
+ rtc_delayed_write(ccr, rtc, RTC_CCR);
|
|
+
|
|
+ return 0;
|
|
+}
|
|
+
|
|
static const struct rtc_class_ops armada38x_rtc_ops = {
|
|
.read_time = armada38x_rtc_read_time,
|
|
.set_time = armada38x_rtc_set_time,
|
|
.read_alarm = armada38x_rtc_read_alarm,
|
|
.set_alarm = armada38x_rtc_set_alarm,
|
|
.alarm_irq_enable = armada38x_rtc_alarm_irq_enable,
|
|
+ .read_offset = armada38x_rtc_read_offset,
|
|
+ .set_offset = armada38x_rtc_set_offset,
|
|
};
|
|
|
|
static const struct rtc_class_ops armada38x_rtc_ops_noirq = {
|
|
.read_time = armada38x_rtc_read_time,
|
|
.set_time = armada38x_rtc_set_time,
|
|
.read_alarm = armada38x_rtc_read_alarm,
|
|
+ .read_offset = armada38x_rtc_read_offset,
|
|
+ .set_offset = armada38x_rtc_set_offset,
|
|
};
|
|
|
|
static const struct armada38x_rtc_data armada38x_data = {
|