OpenWrt – Blame information for rev 4

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4 office 1 commit f94ffbc2c2a4128c4412bb483d0807722dfb682b
2 Author: Russell King <rmk+kernel@armlinux.org.uk>
3 Date: Fri Sep 29 11:23:31 2017 +0100
4  
5 rtc: armada38x: add support for trimming the RTC
6  
7 Add support for trimming the RTC using the offset mechanism. This RTC
8 supports two modes: low update mode and high update mode. Low update
9 mode has finer precision than high update mode, so we use the low mode
10 where possible.
11  
12 Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
13 Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
14  
15 --- a/drivers/rtc/rtc-armada38x.c
16 +++ b/drivers/rtc/rtc-armada38x.c
17 @@ -28,6 +28,8 @@
18 #define RTC_IRQ_AL_EN BIT(0)
19 #define RTC_IRQ_FREQ_EN BIT(1)
20 #define RTC_IRQ_FREQ_1HZ BIT(2)
21 +#define RTC_CCR 0x18
22 +#define RTC_CCR_MODE BIT(15)
23  
24 #define RTC_TIME 0xC
25 #define RTC_ALARM1 0x10
26 @@ -343,18 +345,117 @@ static irqreturn_t armada38x_rtc_alarm_i
27 return IRQ_HANDLED;
28 }
29  
30 +/*
31 + * The information given in the Armada 388 functional spec is complex.
32 + * They give two different formulas for calculating the offset value,
33 + * but when considering "Offset" as an 8-bit signed integer, they both
34 + * reduce down to (we shall rename "Offset" as "val" here):
35 + *
36 + * val = (f_ideal / f_measured - 1) / resolution where f_ideal = 32768
37 + *
38 + * Converting to time, f = 1/t:
39 + * val = (t_measured / t_ideal - 1) / resolution where t_ideal = 1/32768
40 + *
41 + * => t_measured / t_ideal = val * resolution + 1
42 + *
43 + * "offset" in the RTC interface is defined as:
44 + * t = t0 * (1 + offset * 1e-9)
45 + * where t is the desired period, t0 is the measured period with a zero
46 + * offset, which is t_measured above. With t0 = t_measured and t = t_ideal,
47 + * offset = (t_ideal / t_measured - 1) / 1e-9
48 + *
49 + * => t_ideal / t_measured = offset * 1e-9 + 1
50 + *
51 + * so:
52 + *
53 + * offset * 1e-9 + 1 = 1 / (val * resolution + 1)
54 + *
55 + * We want "resolution" to be an integer, so resolution = R * 1e-9, giving
56 + * offset = 1e18 / (val * R + 1e9) - 1e9
57 + * val = (1e18 / (offset + 1e9) - 1e9) / R
58 + * with a common transformation:
59 + * f(x) = 1e18 / (x + 1e9) - 1e9
60 + * offset = f(val * R)
61 + * val = f(offset) / R
62 + *
63 + * Armada 38x supports two modes, fine mode (954ppb) and coarse mode (3815ppb).
64 + */
65 +static long armada38x_ppb_convert(long ppb)
66 +{
67 + long div = ppb + 1000000000L;
68 +
69 + return div_s64(1000000000000000000LL + div / 2, div) - 1000000000L;
70 +}
71 +
72 +static int armada38x_rtc_read_offset(struct device *dev, long *offset)
73 +{
74 + struct armada38x_rtc *rtc = dev_get_drvdata(dev);
75 + unsigned long ccr, flags;
76 + long ppb_cor;
77 +
78 + spin_lock_irqsave(&rtc->lock, flags);
79 + ccr = rtc->data->read_rtc_reg(rtc, RTC_CCR);
80 + spin_unlock_irqrestore(&rtc->lock, flags);
81 +
82 + ppb_cor = (ccr & RTC_CCR_MODE ? 3815 : 954) * (s8)ccr;
83 + /* ppb_cor + 1000000000L can never be zero */
84 + *offset = armada38x_ppb_convert(ppb_cor);
85 +
86 + return 0;
87 +}
88 +
89 +static int armada38x_rtc_set_offset(struct device *dev, long offset)
90 +{
91 + struct armada38x_rtc *rtc = dev_get_drvdata(dev);
92 + unsigned long ccr = 0;
93 + long ppb_cor, off;
94 +
95 + /*
96 + * The maximum ppb_cor is -128 * 3815 .. 127 * 3815, but we
97 + * need to clamp the input. This equates to -484270 .. 488558.
98 + * Not only is this to stop out of range "off" but also to
99 + * avoid the division by zero in armada38x_ppb_convert().
100 + */
101 + offset = clamp(offset, -484270L, 488558L);
102 +
103 + ppb_cor = armada38x_ppb_convert(offset);
104 +
105 + /*
106 + * Use low update mode where possible, which gives a better
107 + * resolution of correction.
108 + */
109 + off = DIV_ROUND_CLOSEST(ppb_cor, 954);
110 + if (off > 127 || off < -128) {
111 + ccr = RTC_CCR_MODE;
112 + off = DIV_ROUND_CLOSEST(ppb_cor, 3815);
113 + }
114 +
115 + /*
116 + * Armada 388 requires a bit pattern in bits 14..8 depending on
117 + * the sign bit: { 0, ~S, S, S, S, S, S }
118 + */
119 + ccr |= (off & 0x3fff) ^ 0x2000;
120 + rtc_delayed_write(ccr, rtc, RTC_CCR);
121 +
122 + return 0;
123 +}
124 +
125 static const struct rtc_class_ops armada38x_rtc_ops = {
126 .read_time = armada38x_rtc_read_time,
127 .set_time = armada38x_rtc_set_time,
128 .read_alarm = armada38x_rtc_read_alarm,
129 .set_alarm = armada38x_rtc_set_alarm,
130 .alarm_irq_enable = armada38x_rtc_alarm_irq_enable,
131 + .read_offset = armada38x_rtc_read_offset,
132 + .set_offset = armada38x_rtc_set_offset,
133 };
134  
135 static const struct rtc_class_ops armada38x_rtc_ops_noirq = {
136 .read_time = armada38x_rtc_read_time,
137 .set_time = armada38x_rtc_set_time,
138 .read_alarm = armada38x_rtc_read_alarm,
139 + .read_offset = armada38x_rtc_read_offset,
140 + .set_offset = armada38x_rtc_set_offset,
141 };
142  
143 static const struct armada38x_rtc_data armada38x_data = {