arch/mips/generic/board-ranchu.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Support code for virtual Ranchu board for MIPS.
   4  *
   5  * Author: Miodrag Dinic <miodrag.dinic@mips.com>
   6  */
   7
   8 #include <linux/of_address.h>
   9 #include <linux/types.h>
  10
  11 #include <asm/machine.h>
  12 #include <asm/mipsregs.h>
  13 #include <asm/time.h>
  14
  15 #define GOLDFISH_TIMER_LOW              0x00
  16 #define GOLDFISH_TIMER_HIGH             0x04
  17
  18 static __init u64 read_rtc_time(void __iomem *base)
  19 {
  20         u32 time_low;
  21         u32 time_high;
  22
  23         /*
  24          * Reading the low address latches the high value
  25          * as well so there is no fear that we may read
  26          * inaccurate high value.
  27          */
  28         time_low = readl(base + GOLDFISH_TIMER_LOW);
  29         time_high = readl(base + GOLDFISH_TIMER_HIGH);
  30
  31         return ((u64)time_high << 32) | time_low;
  32 }
  33
  34 static __init unsigned int ranchu_measure_hpt_freq(void)
  35 {
  36         u64 rtc_start, rtc_current, rtc_delta;
  37         unsigned int start, count;
  38         struct device_node *np;
  39         void __iomem *rtc_base;
  40
  41         np = of_find_compatible_node(NULL, NULL, "google,goldfish-rtc");
  42         if (!np)
  43                 panic("%s(): Failed to find 'google,goldfish-rtc' dt node!",
  44                       __func__);
  45
  46         rtc_base = of_iomap(np, 0);
  47         if (!rtc_base)
  48                 panic("%s(): Failed to ioremap Goldfish RTC base!", __func__);
  49
  50         /*
  51          * Poll the nanosecond resolution RTC for one
  52          * second to calibrate the CPU frequency.
  53          */
  54         rtc_start = read_rtc_time(rtc_base);
  55         start = read_c0_count();
  56
  57         do {
  58                 rtc_current = read_rtc_time(rtc_base);
  59                 rtc_delta = rtc_current - rtc_start;
  60         } while (rtc_delta < NSEC_PER_SEC);
  61
  62         count = read_c0_count() - start;
  63
  64         /*
  65          * Make sure the frequency will be a round number.
  66          * Without this correction, the returned value may vary
  67          * between subsequent emulation executions.
  68          *
  69          * TODO: Set this value using device tree.
  70          */
  71         count += 5000;
  72         count -= count % 10000;
  73
  74         iounmap(rtc_base);
  75
  76         return count;
  77 }
  78
  79 static const struct of_device_id ranchu_of_match[] __initconst = {
  80         {
  81                 .compatible = "mti,ranchu",
  82         },
  83         {}
  84 };
  85
  86 MIPS_MACHINE(ranchu) = {
  87         .matches = ranchu_of_match,
  88         .measure_hpt_freq = ranchu_measure_hpt_freq,
  89 };