drivers/staging/greybus/timesync_platform.c

   1 /*
   2  * TimeSync API driver.
   3  *
   4  * Copyright 2016 Google Inc.
   5  * Copyright 2016 Linaro Ltd.
   6  *
   7  * Released under the GPLv2 only.
   8  *
   9  * This code reads directly from an ARMv7 memory-mapped timer that lives in
  10  * MMIO space. Since this counter lives inside of MMIO space its shared between
  11  * cores and that means we don't have to worry about issues like TSC on x86
  12  * where each time-stamp-counter (TSC) is local to a particular core.
  13  *
  14  * Register-level access code is based on
  15  * drivers/clocksource/arm_arch_timer.c
  16  */
  17 #include <linux/cpufreq.h>
  18 #include <linux/of_platform.h>
  19
  20 #include "greybus.h"
  21 #include "arche_platform.h"
  22
  23 #define DEFAULT_FRAMETIME_CLOCK_HZ 19200000
  24
  25 static u32 gb_timesync_clock_frequency;
  26 int (*arche_platform_change_state_cb)(enum arche_platform_state state,
  27                                       struct gb_timesync_svc *pdata);
  28 EXPORT_SYMBOL_GPL(arche_platform_change_state_cb);
  29
  30 u64 gb_timesync_platform_get_counter(void)
  31 {
  32         return (u64)get_cycles();
  33 }
  34
  35 u32 gb_timesync_platform_get_clock_rate(void)
  36 {
  37         if (unlikely(!gb_timesync_clock_frequency)) {
  38                 gb_timesync_clock_frequency = cpufreq_get(0);
  39                 if (!gb_timesync_clock_frequency)
  40                         gb_timesync_clock_frequency = DEFAULT_FRAMETIME_CLOCK_HZ;
  41         }
  42
  43         return gb_timesync_clock_frequency;
  44 }
  45
  46 int gb_timesync_platform_lock_bus(struct gb_timesync_svc *pdata)
  47 {
  48         return arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_TIME_SYNC,
  49                                               pdata);
  50 }
  51
  52 void gb_timesync_platform_unlock_bus(void)
  53 {
  54         arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_ACTIVE, NULL);
  55 }
  56
  57 static const struct of_device_id arch_timer_of_match[] = {
  58         { .compatible   = "google,greybus-frame-time-counter", },
  59         {},
  60 };
  61
  62 int __init gb_timesync_platform_init(void)
  63 {
  64         struct device_node *np;
  65
  66         np = of_find_matching_node(NULL, arch_timer_of_match);
  67         if (!np) {
  68                 /* Tolerate not finding to allow BBB etc to continue */
  69                 pr_warn("Unable to find a compatible ARMv7 timer\n");
  70                 return 0;
  71         }
  72
  73         if (of_property_read_u32(np, "clock-frequency",
  74                                  &gb_timesync_clock_frequency)) {
  75                 pr_err("Unable to find timer clock-frequency\n");
  76                 return -ENODEV;
  77         }
  78
  79         return 0;
  80 }
  81
  82 void gb_timesync_platform_exit(void) {}