设备树学习之（六）RTC

开发板：tiny4412SDK + S702 + 4GB Flash 
要移植的内核版本：Linux-4.4.0 （支持device tree） 
u-boot版本：友善之臂自带的 U-Boot 2010.12 
busybox版本：busybox 1.25

目标： 
Linux4.4 中已经对 tiny4412 rtc 有了支持，但是使能设备树之后启动报错，简单修改，使 rtc 正常工作。

设备树：

    rtc: rtc@10070000 {        compatible = "samsung,s3c6410-rtc";        reg = <0x10070000 0x100>;        interrupt-parent = <&pmu_system_controller>;//注释掉此行        interrupts = <0 44 0>, <0 45 0>;        clocks = <&clock CLK_RTC>;        clock-names = "rtc";        status = "disabled";    };
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启动错误信息：

[    2.193630] s3c-rtc 10070000.rtc: failed to find rtc source clock            [    2.198950] s3c-rtc: probe of 10070000.rtc failed with error -2  
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简单修改：

修改：driver/rtc/rtc-s3c.c注释掉以下代码/*    if (info->data->needs_src_clk) {        info->rtc_src_clk = devm_clk_get(&pdev->dev, "rtc_src");        if (IS_ERR(info->rtc_src_clk)) {            dev_err(&pdev->dev,                "failed to find rtc source clock\n");            clk_disable_unprepare(info->rtc_clk);            return PTR_ERR(info->rtc_src_clk);        }        clk_prepare_enable(info->rtc_src_clk);    }*/或者修改：static struct s3c_rtc_data const s3c6410_rtc_data = {    .max_user_freq      = 32768,    .needs_src_clk      = true, //修改为false    .irq_handler        = s3c6410_rtc_irq,    .set_freq           = s3c6410_rtc_setfreq,    .enable_tick        = s3c6410_rtc_enable_tick,    .save_tick_cnt      = s3c6410_rtc_save_tick_cnt,    .restore_tick_cnt   = s3c6410_rtc_restore_tick_cnt,    .enable         = s3c24xx_rtc_enable,    .disable        = s3c6410_rtc_disable,};
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linux 下更改系统时间：

date: invalid option -- 'h'                                                     BusyBox v1.25.0 (2016-12-16 21:42:21 ULAT) multi-call binary.                   Usage: date [OPTIONS] [+FMT] [TIME]                                             Display time (using +FMT), or set time                                                  [-s,--set] TIME Set time to TIME                                                -u,--utc        Work in UTC (don't convert to local time)                       -R,--rfc-2822   Output RFC-2822 compliant date string                           -I[SPEC]        Output ISO-8601 compliant date string                                           SPEC='date' (default) for date only,                                            'hours', 'minutes', or 'seconds' for date and                                   time to the indicated precision                                 -r,--reference FILE     Display last modification time of FILE                  -d,--date TIME  Display TIME, not 'now'                                         -D FMT          Use FMT for -d TIME conversion                          Recognized TIME formats:                                                                hh:mm[:ss]                                                                      [YYYY.]MM.DD-hh:mm[:ss]                                                         YYYY-MM-DD hh:mm[:ss]                                                           [[[[[YY]YY]MM]DD]hh]mm[.ss]                                                     'date TIME' form accepts MMDDhhmm[[YY]YY][.ss] instead                  date -s 2017-01-01date -s 22:50:00
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系统时间和硬件rtc的同步：

/ # hwclock -h                                                                  hwclock: invalid option -- 'h'                                                  BusyBox v1.25.0 (2016-12-16 21:42:21 ULAT) multi-call binary.                   Usage: hwclock [-r|--show] [-s|--hctosys] [-w|--systohc] [-t|--systz] [-l|--loc]Query and set hardware clock (RTC)                                                      -r      Show hardware clock time                                                -s      Set system time from hardware clock                                     -w      Set hardware clock from system time                                     -t      Set in-kernel timezone, correct system time                                     if hardware clock is in local time                                      -u      Assume hardware clock is kept in UTC                                    -l      Assume hardware clock is kept in local time                             -f FILE Use specified device (e.g. /dev/rtc2)