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