1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Support code for virtual Ranchu board for MIPS.
4 *
5 * Author: Miodrag Dinic <miodrag.dinic@mips.com>
6 */
7
8 #include <linux/of_address.h>
9 #include <linux/types.h>
10
11 #include <asm/machine.h>
12 #include <asm/mipsregs.h>
13 #include <asm/time.h>
14
15 #define GOLDFISH_TIMER_LOW 0x00
16 #define GOLDFISH_TIMER_HIGH 0x04
17
18 static __init u64 read_rtc_time(void __iomem *base)
19 {
20 u32 time_low;
21 u32 time_high;
22
23 /*
24 * Reading the low address latches the high value
25 * as well so there is no fear that we may read
26 * inaccurate high value.
27 */
28 time_low = readl(base + GOLDFISH_TIMER_LOW);
29 time_high = readl(base + GOLDFISH_TIMER_HIGH);
30
31 return ((u64)time_high << 32) | time_low;
32 }
33
34 static __init unsigned int ranchu_measure_hpt_freq(void)
35 {
36 u64 rtc_start, rtc_current, rtc_delta;
37 unsigned int start, count;
38 struct device_node *np;
39 void __iomem *rtc_base;
40
41 np = of_find_compatible_node(NULL, NULL, "google,goldfish-rtc");
42 if (!np)
43 panic("%s(): Failed to find 'google,goldfish-rtc' dt node!",
44 __func__);
45
46 rtc_base = of_iomap(np, 0);
47 of_node_put(np);
48 if (!rtc_base)
49 panic("%s(): Failed to ioremap Goldfish RTC base!", __func__);
50
51 /*
52 * Poll the nanosecond resolution RTC for one
53 * second to calibrate the CPU frequency.
54 */
55 rtc_start = read_rtc_time(rtc_base);
56 start = read_c0_count();
57
58 do {
59 rtc_current = read_rtc_time(rtc_base);
60 rtc_delta = rtc_current - rtc_start;
61 } while (rtc_delta < NSEC_PER_SEC);
62
63 count = read_c0_count() - start;
64
65 /*
66 * Make sure the frequency will be a round number.
67 * Without this correction, the returned value may vary
68 * between subsequent emulation executions.
69 *
70 * TODO: Set this value using device tree.
71 */
72 count += 5000;
73 count -= count % 10000;
74
75 iounmap(rtc_base);
76
77 return count;
78 }
79
80 static const struct of_device_id ranchu_of_match[] __initconst = {
81 {
82 .compatible = "mti,ranchu",
83 },
84 {}
85 };
86
87 MIPS_MACHINE(ranchu) = {
88 .matches = ranchu_of_match,
89 .measure_hpt_freq = ranchu_measure_hpt_freq,
90 };
91
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