[LEDE-DEV] [PATCH 1/2] mvebu: Backport RTC trimming support.
Rosen Penev
rosenp at gmail.com
Thu Mar 15 17:53:26 PDT 2018
This enables a higher precision mode for the RTC.
Signed-off-by: Rosen Penev <rosenp at gmail.com>
---
.../patches-4.14/420-rtc-trimming-support.patch | 145 +++++++++++++++++++++
1 file changed, 145 insertions(+)
create mode 100644 target/linux/mvebu/patches-4.14/420-rtc-trimming-support.patch
diff --git a/target/linux/mvebu/patches-4.14/420-rtc-trimming-support.patch b/target/linux/mvebu/patches-4.14/420-rtc-trimming-support.patch
new file mode 100644
index 0000000000..43d9857336
--- /dev/null
+++ b/target/linux/mvebu/patches-4.14/420-rtc-trimming-support.patch
@@ -0,0 +1,145 @@
+commit f94ffbc2c2a4128c4412bb483d0807722dfb682b
+Author: Russell King <rmk+kernel at 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 at armlinux.org.uk>
+ Signed-off-by: Alexandre Belloni <alexandre.belloni at free-electrons.com>
+
+diff --git a/drivers/rtc/rtc-armada38x.c b/drivers/rtc/rtc-armada38x.c
+index 21f355c..1e4978c 100644
+--- 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_irq(int irq, void *data)
+ 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 = {
--
2.16.2
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