arch/sh/boards/mach-dreamcast/rtc.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * arch/sh/boards/dreamcast/rtc.c
   4  *
   5  * Dreamcast AICA RTC routines.
   6  *
   7  * Copyright (c) 2001, 2002 M. R. Brown <mrbrown@0xd6.org>
   8  * Copyright (c) 2002 Paul Mundt <lethal@chaoticdreams.org>
   9  */
  10
  11 #include <linux/time.h>
  12 #include <linux/rtc.h>
  13 #include <linux/io.h>
  14 #include <linux/platform_device.h>
  15
  16 /* The AICA RTC has an Epoch of 1/1/1950, so we must subtract 20 years (in
  17    seconds) to get the standard Unix Epoch when getting the time, and add
  18    20 years when setting the time. */
  19 #define TWENTY_YEARS ((20 * 365LU + 5) * 86400)
  20
  21 /* The AICA RTC is represented by a 32-bit seconds counter stored in 2 16-bit
  22    registers.*/
  23 #define AICA_RTC_SECS_H         0xa0710000
  24 #define AICA_RTC_SECS_L         0xa0710004
  25
  26 /**
  27  * aica_rtc_gettimeofday - Get the time from the AICA RTC
  28  * @dev: the RTC device (ignored)
  29  * @tm: pointer to resulting RTC time structure
  30  *
  31  * Grabs the current RTC seconds counter and adjusts it to the Unix Epoch.
  32  */
  33 static int aica_rtc_gettimeofday(struct device *dev, struct rtc_time *tm)
  34 {
  35         unsigned long val1, val2;
  36         time64_t t;
  37
  38         do {
  39                 val1 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
  40                         (__raw_readl(AICA_RTC_SECS_L) & 0xffff);
  41
  42                 val2 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
  43                         (__raw_readl(AICA_RTC_SECS_L) & 0xffff);
  44         } while (val1 != val2);
  45
  46         /* normalize to 1970..2106 time range */
  47         t = (u32)(val1 - TWENTY_YEARS);
  48
  49         rtc_time64_to_tm(t, tm);
  50
  51         return 0;
  52 }
  53
  54 /**
  55  * aica_rtc_settimeofday - Set the AICA RTC to the current time
  56  * @dev: the RTC device (ignored)
  57  * @tm: pointer to new RTC time structure
  58  *
  59  * Adjusts the given @tv to the AICA Epoch and sets the RTC seconds counter.
  60  */
  61 static int aica_rtc_settimeofday(struct device *dev, struct rtc_time *tm)
  62 {
  63         unsigned long val1, val2;
  64         time64_t secs = rtc_tm_to_time64(tm);
  65         u32 adj = secs + TWENTY_YEARS;
  66
  67         do {
  68                 __raw_writel((adj & 0xffff0000) >> 16, AICA_RTC_SECS_H);
  69                 __raw_writel((adj & 0xffff), AICA_RTC_SECS_L);
  70
  71                 val1 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
  72                         (__raw_readl(AICA_RTC_SECS_L) & 0xffff);
  73
  74                 val2 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
  75                         (__raw_readl(AICA_RTC_SECS_L) & 0xffff);
  76         } while (val1 != val2);
  77
  78         return 0;
  79 }
  80
  81 static const struct rtc_class_ops rtc_generic_ops = {
  82         .read_time = aica_rtc_gettimeofday,
  83         .set_time = aica_rtc_settimeofday,
  84 };
  85
  86 static int __init aica_time_init(void)
  87 {
  88         struct platform_device *pdev;
  89
  90         pdev = platform_device_register_data(NULL, "rtc-generic", -1,
  91                                              &rtc_generic_ops,
  92                                              sizeof(rtc_generic_ops));
  93
  94         return PTR_ERR_OR_ZERO(pdev);
  95 }
  96 arch_initcall(aica_time_init);