arch/mips/generic/board-ranchu.c

   1 /*
   2  * Support code for virtual Ranchu board for MIPS.
   3  *
   4  * Author: Miodrag Dinic <miodrag.dinic@mips.com>
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License as published by the
   8  * Free Software Foundation;  either version 2 of the  License, or (at your
   9  * option) any later version.
  10  */
  11
  12 #include <linux/of_address.h>
  13 #include <linux/types.h>
  14
  15 #include <asm/machine.h>
  16 #include <asm/mipsregs.h>
  17 #include <asm/time.h>
  18
  19 #define GOLDFISH_TIMER_LOW              0x00
  20 #define GOLDFISH_TIMER_HIGH             0x04
  21
  22 static __init u64 read_rtc_time(void __iomem *base)
  23 {
  24         u32 time_low;
  25         u32 time_high;
  26
  27         /*
  28          * Reading the low address latches the high value
  29          * as well so there is no fear that we may read
  30          * inaccurate high value.
  31          */
  32         time_low = readl(base + GOLDFISH_TIMER_LOW);
  33         time_high = readl(base + GOLDFISH_TIMER_HIGH);
  34
  35         return ((u64)time_high << 32) | time_low;
  36 }
  37
  38 static __init unsigned int ranchu_measure_hpt_freq(void)
  39 {
  40         u64 rtc_start, rtc_current, rtc_delta;
  41         unsigned int start, count;
  42         struct device_node *np;
  43         void __iomem *rtc_base;
  44
  45         np = of_find_compatible_node(NULL, NULL, "google,goldfish-rtc");
  46         if (!np)
  47                 panic("%s(): Failed to find 'google,goldfish-rtc' dt node!",
  48                       __func__);
  49
  50         rtc_base = of_iomap(np, 0);
  51         if (!rtc_base)
  52                 panic("%s(): Failed to ioremap Goldfish RTC base!", __func__);
  53
  54         /*
  55          * Poll the nanosecond resolution RTC for one
  56          * second to calibrate the CPU frequency.
  57          */
  58         rtc_start = read_rtc_time(rtc_base);
  59         start = read_c0_count();
  60
  61         do {
  62                 rtc_current = read_rtc_time(rtc_base);
  63                 rtc_delta = rtc_current - rtc_start;
  64         } while (rtc_delta < NSEC_PER_SEC);
  65
  66         count = read_c0_count() - start;
  67
  68         /*
  69          * Make sure the frequency will be a round number.
  70          * Without this correction, the returned value may vary
  71          * between subsequent emulation executions.
  72          *
  73          * TODO: Set this value using device tree.
  74          */
  75         count += 5000;
  76         count -= count % 10000;
  77
  78         iounmap(rtc_base);
  79
  80         return count;
  81 }
  82
  83 static const struct of_device_id ranchu_of_match[] __initconst = {
  84         {
  85                 .compatible = "mti,ranchu",
  86         },
  87         {}
  88 };
  89
  90 MIPS_MACHINE(ranchu) = {
  91         .matches = ranchu_of_match,
  92         .measure_hpt_freq = ranchu_measure_hpt_freq,
  93 };