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	if (!rtc_base)
48		panic("%s(): Failed to ioremap Goldfish RTC base!", __func__);
49
50	/*
51	 * Poll the nanosecond resolution RTC for one
52	 * second to calibrate the CPU frequency.
53	 */
54	rtc_start = read_rtc_time(rtc_base);
55	start = read_c0_count();
56
57	do {
58		rtc_current = read_rtc_time(rtc_base);
59		rtc_delta = rtc_current - rtc_start;
60	} while (rtc_delta < NSEC_PER_SEC);
61
62	count = read_c0_count() - start;
63
64	/*
65	 * Make sure the frequency will be a round number.
66	 * Without this correction, the returned value may vary
67	 * between subsequent emulation executions.
68	 *
69	 * TODO: Set this value using device tree.
70	 */
71	count += 5000;
72	count -= count % 10000;
73
74	iounmap(rtc_base);
75
76	return count;
77}
78
79static const struct of_device_id ranchu_of_match[] __initconst = {
80	{
81		.compatible = "mti,ranchu",
82	},
83	{}
84};
85
86MIPS_MACHINE(ranchu) = {
87	.matches = ranchu_of_match,
88	.measure_hpt_freq = ranchu_measure_hpt_freq,
89};