1 /*
2  * Copyright (C) Maxime Coquelin 2015
3  * Author:  Maxime Coquelin <mcoquelin.stm32@gmail.com>
4  * License terms:  GNU General Public License (GPL), version 2
5  */
6 
7 #include <linux/kernel.h>
8 #include <linux/clocksource.h>
9 #include <linux/clockchips.h>
10 #include <linux/io.h>
11 #include <linux/of.h>
12 #include <linux/of_address.h>
13 #include <linux/clk.h>
14 #include <linux/bitops.h>
15 
16 #define SYST_CSR	0x00
17 #define SYST_RVR	0x04
18 #define SYST_CVR	0x08
19 #define SYST_CALIB	0x0c
20 
21 #define SYST_CSR_ENABLE BIT(0)
22 
23 #define SYSTICK_LOAD_RELOAD_MASK 0x00FFFFFF
24 
25 static int __init system_timer_of_register(struct device_node *np)
26 {
27 	struct clk *clk = NULL;
28 	void __iomem *base;
29 	u32 rate;
30 	int ret;
31 
32 	base = of_iomap(np, 0);
33 	if (!base) {
34 		pr_warn("system-timer: invalid base address\n");
35 		return -ENXIO;
36 	}
37 
38 	ret = of_property_read_u32(np, "clock-frequency", &rate);
39 	if (ret) {
40 		clk = of_clk_get(np, 0);
41 		if (IS_ERR(clk)) {
42 			ret = PTR_ERR(clk);
43 			goto out_unmap;
44 		}
45 
46 		ret = clk_prepare_enable(clk);
47 		if (ret)
48 			goto out_clk_put;
49 
50 		rate = clk_get_rate(clk);
51 		if (!rate) {
52 			ret = -EINVAL;
53 			goto out_clk_disable;
54 		}
55 	}
56 
57 	writel_relaxed(SYSTICK_LOAD_RELOAD_MASK, base + SYST_RVR);
58 	writel_relaxed(SYST_CSR_ENABLE, base + SYST_CSR);
59 
60 	ret = clocksource_mmio_init(base + SYST_CVR, "arm_system_timer", rate,
61 			200, 24, clocksource_mmio_readl_down);
62 	if (ret) {
63 		pr_err("failed to init clocksource (%d)\n", ret);
64 		if (clk)
65 			goto out_clk_disable;
66 		else
67 			goto out_unmap;
68 	}
69 
70 	pr_info("ARM System timer initialized as clocksource\n");
71 
72 	return 0;
73 
74 out_clk_disable:
75 	clk_disable_unprepare(clk);
76 out_clk_put:
77 	clk_put(clk);
78 out_unmap:
79 	iounmap(base);
80 	pr_warn("ARM System timer register failed (%d)\n", ret);
81 
82 	return ret;
83 }
84 
85 CLOCKSOURCE_OF_DECLARE(arm_systick, "arm,armv7m-systick",
86 			system_timer_of_register);
87