drivers/clocksource/armv7m_systick.c

   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);