xref: /openbmc/linux/arch/mips/generic/board-ranchu.c (revision 4becf641)
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 
read_rtc_time(void __iomem * base)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 
ranchu_measure_hpt_freq(void)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