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
18static __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
34static __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
80static const struct of_device_id ranchu_of_match[] __initconst = {
81	{
82		.compatible = "mti,ranchu",
83	},
84	{}
85};
86
87MIPS_MACHINE(ranchu) = {
88	.matches = ranchu_of_match,
89	.measure_hpt_freq = ranchu_measure_hpt_freq,
90};
91