rtc: armada38x: add support for trimming the RTC (f94ffbc2) · Commits · 戴 / test

drivers/rtc/rtc-armada38x.c

+101 −0

Original line number	Original line	Diff line number	Diff line
	@@ -28,6 +28,8 @@
	#define RTC_IRQ_AL_EN BIT(0)		#define RTC_IRQ_AL_EN BIT(0)
	#define RTC_IRQ_FREQ_EN BIT(1)		#define RTC_IRQ_FREQ_EN BIT(1)
	#define RTC_IRQ_FREQ_1HZ BIT(2)		#define RTC_IRQ_FREQ_1HZ BIT(2)
			#define RTC_CCR 0x18
			#define RTC_CCR_MODE BIT(15)

	#define RTC_TIME 0xC		#define RTC_TIME 0xC
	#define RTC_ALARM1 0x10		#define RTC_ALARM1 0x10
	@@ -343,18 +345,117 @@ static irqreturn_t armada38x_rtc_alarm_irq(int irq, void *data)
	return IRQ_HANDLED;		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 = {		static const struct rtc_class_ops armada38x_rtc_ops = {
	.read_time = armada38x_rtc_read_time,		.read_time = armada38x_rtc_read_time,
	.set_time = armada38x_rtc_set_time,		.set_time = armada38x_rtc_set_time,
	.read_alarm = armada38x_rtc_read_alarm,		.read_alarm = armada38x_rtc_read_alarm,
	.set_alarm = armada38x_rtc_set_alarm,		.set_alarm = armada38x_rtc_set_alarm,
	.alarm_irq_enable = armada38x_rtc_alarm_irq_enable,		.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 = {		static const struct rtc_class_ops armada38x_rtc_ops_noirq = {
	.read_time = armada38x_rtc_read_time,		.read_time = armada38x_rtc_read_time,
	.set_time = armada38x_rtc_set_time,		.set_time = armada38x_rtc_set_time,
	.read_alarm = armada38x_rtc_read_alarm,		.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 = {		static const struct armada38x_rtc_data armada38x_data = {

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