diff options
Diffstat (limited to 'target/linux/mvebu/patches-4.14/420-rtc-trimming-support.patch')
| -rw-r--r-- | target/linux/mvebu/patches-4.14/420-rtc-trimming-support.patch | 143 |
1 files changed, 143 insertions, 0 deletions
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..2974a69760 --- /dev/null +++ b/target/linux/mvebu/patches-4.14/420-rtc-trimming-support.patch @@ -0,0 +1,143 @@ +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 = { |