LXR linux/drivers/rtc/rtc-dm355evm.c

   1// SPDX-License-Identifier: GPL-2.0+
   2/*
   3 * rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
   4 *
   5 * Copyright (c) 2008 by David Brownell
   6 */
   7#include <linux/kernel.h>
   8#include <linux/init.h>
   9#include <linux/rtc.h>
  10#include <linux/platform_device.h>
  11
  12#include <linux/mfd/dm355evm_msp.h>
  13#include <linux/module.h>
  14
  15
  16/*
  17 * The MSP430 firmware on the DM355 EVM uses a watch crystal to feed
  18 * a 1 Hz counter.  When a backup battery is supplied, that makes a
  19 * reasonable RTC for applications where alarms and non-NTP drift
  20 * compensation aren't important.
  21 *
  22 * The only real glitch is the inability to read or write all four
  23 * counter bytes atomically:  the count may increment in the middle
  24 * of an operation, causing trouble when the LSB rolls over.
  25 *
  26 * This driver was tested with firmware revision A4.
  27 */
  28union evm_time {
  29        u8      bytes[4];
  30        u32     value;
  31};
  32
  33static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm)
  34{
  35        union evm_time  time;
  36        int             status;
  37        int             tries = 0;
  38
  39        do {
  40                /*
  41                 * Read LSB(0) to MSB(3) bytes.  Defend against the counter
  42                 * rolling over by re-reading until the value is stable,
  43                 * and assuming the four reads take at most a few seconds.
  44                 */
  45                status = dm355evm_msp_read(DM355EVM_MSP_RTC_0);
  46                if (status < 0)
  47                        return status;
  48                if (tries && time.bytes[0] == status)
  49                        break;
  50                time.bytes[0] = status;
  51
  52                status = dm355evm_msp_read(DM355EVM_MSP_RTC_1);
  53                if (status < 0)
  54                        return status;
  55                if (tries && time.bytes[1] == status)
  56                        break;
  57                time.bytes[1] = status;
  58
  59                status = dm355evm_msp_read(DM355EVM_MSP_RTC_2);
  60                if (status < 0)
  61                        return status;
  62                if (tries && time.bytes[2] == status)
  63                        break;
  64                time.bytes[2] = status;
  65
  66                status = dm355evm_msp_read(DM355EVM_MSP_RTC_3);
  67                if (status < 0)
  68                        return status;
  69                if (tries && time.bytes[3] == status)
  70                        break;
  71                time.bytes[3] = status;
  72
  73        } while (++tries < 5);
  74
  75        dev_dbg(dev, "read timestamp %08x\n", time.value);
  76
  77        rtc_time64_to_tm(le32_to_cpu(time.value), tm);
  78        return 0;
  79}
  80
  81static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm)
  82{
  83        union evm_time  time;
  84        unsigned long   value;
  85        int             status;
  86
  87        value = rtc_tm_to_time64(tm);
  88        time.value = cpu_to_le32(value);
  89
  90        dev_dbg(dev, "write timestamp %08x\n", time.value);
  91
  92        /*
  93         * REVISIT handle non-atomic writes ... maybe just retry until
  94         * byte[1] sticks (no rollover)?
  95         */
  96        status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
  97        if (status < 0)
  98                return status;
  99
 100        status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
 101        if (status < 0)
 102                return status;
 103
 104        status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
 105        if (status < 0)
 106                return status;
 107
 108        status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
 109        if (status < 0)
 110                return status;
 111
 112        return 0;
 113}
 114
 115static const struct rtc_class_ops dm355evm_rtc_ops = {
 116        .read_time      = dm355evm_rtc_read_time,
 117        .set_time       = dm355evm_rtc_set_time,
 118};
 119
 120/*----------------------------------------------------------------------*/
 121
 122static int dm355evm_rtc_probe(struct platform_device *pdev)
 123{
 124        struct rtc_device *rtc;
 125
 126        rtc = devm_rtc_allocate_device(&pdev->dev);
 127        if (IS_ERR(rtc))
 128                return PTR_ERR(rtc);
 129
 130        platform_set_drvdata(pdev, rtc);
 131
 132        rtc->ops = &dm355evm_rtc_ops;
 133        rtc->range_max = U32_MAX;
 134
 135        return devm_rtc_register_device(rtc);
 136}
 137
 138/*
 139 * I2C is used to talk to the MSP430, but this platform device is
 140 * exposed by an MFD driver that manages I2C communications.
 141 */
 142static struct platform_driver rtc_dm355evm_driver = {
 143        .probe          = dm355evm_rtc_probe,
 144        .driver         = {
 145                .name   = "rtc-dm355evm",
 146        },
 147};
 148
 149module_platform_driver(rtc_dm355evm_driver);
 150
 151MODULE_LICENSE("GPL");
 152