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    SubjectPATCH: /proc/acpi/alarm: handle day-of-month wraparound on readback
    Fix month wrap issue with readback from /proc/acpi/alarm
    This bug has been around *forever*.

    $ echo '2008-12-01 10:36:20' > /proc/acpi/alarm
    $ cat /proc/acpi/alarm
    2008-11-01 10:36:20

    Note how the readback above shows the month incorrectly.
    But with this patch applied, it shows the correct month (12).

    Patch applies/works on kernels 2.6.25.* through 2.6.27.*,
    and probably on earlier kernels as well.

    Probably best to queue it up for the next major cycle.

    Signed-off-by: Mark Lord <mlord@pobox.com>

    --- linux-2.6.25/drivers/acpi/sleep/proc.c 2008-06-09 14:27:19.000000000 -0400
    +++ linux/drivers/acpi/sleep/proc.c 2008-11-30 18:08:31.000000000 -0500
    @@ -84,12 +84,15 @@
    #define HAVE_ACPI_LEGACY_ALARM
    #endif

    +static u32 cmos_bcd_read(int offset, int rtc_control);
    +
    #ifdef HAVE_ACPI_LEGACY_ALARM

    static int acpi_system_alarm_seq_show(struct seq_file *seq, void *offset)
    {
    u32 sec, min, hr;
    u32 day, mo, yr, cent = 0;
    + u32 today = 0;
    unsigned char rtc_control = 0;
    unsigned long flags;

    @@ -97,38 +100,32 @@

    spin_lock_irqsave(&rtc_lock, flags);

    - sec = CMOS_READ(RTC_SECONDS_ALARM);
    - min = CMOS_READ(RTC_MINUTES_ALARM);
    - hr = CMOS_READ(RTC_HOURS_ALARM);
    rtc_control = CMOS_READ(RTC_CONTROL);
    + sec = cmos_bcd_read(RTC_SECONDS_ALARM, rtc_control);
    + min = cmos_bcd_read(RTC_MINUTES_ALARM, rtc_control);
    + hr = cmos_bcd_read(RTC_HOURS_ALARM, rtc_control);

    /* If we ever get an FACP with proper values... */
    - if (acpi_gbl_FADT.day_alarm)
    + if (acpi_gbl_FADT.day_alarm) {
    /* ACPI spec: only low 6 its should be cared */
    day = CMOS_READ(acpi_gbl_FADT.day_alarm) & 0x3F;
    - else
    - day = CMOS_READ(RTC_DAY_OF_MONTH);
    + if (!(rtc_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
    + BCD_TO_BIN(day);
    + } else
    + day = cmos_bcd_read(RTC_DAY_OF_MONTH, rtc_control);
    if (acpi_gbl_FADT.month_alarm)
    - mo = CMOS_READ(acpi_gbl_FADT.month_alarm);
    - else
    - mo = CMOS_READ(RTC_MONTH);
    + mo = cmos_bcd_read(acpi_gbl_FADT.month_alarm, rtc_control);
    + else {
    + mo = cmos_bcd_read(RTC_MONTH, rtc_control);
    + today = cmos_bcd_read(RTC_DAY_OF_MONTH, rtc_control);
    + }
    if (acpi_gbl_FADT.century)
    - cent = CMOS_READ(acpi_gbl_FADT.century);
    + cent = cmos_bcd_read(acpi_gbl_FADT.century, rtc_control);

    - yr = CMOS_READ(RTC_YEAR);
    + yr = cmos_bcd_read(RTC_YEAR, rtc_control);

    spin_unlock_irqrestore(&rtc_lock, flags);

    - if (!(rtc_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
    - BCD_TO_BIN(sec);
    - BCD_TO_BIN(min);
    - BCD_TO_BIN(hr);
    - BCD_TO_BIN(day);
    - BCD_TO_BIN(mo);
    - BCD_TO_BIN(yr);
    - BCD_TO_BIN(cent);
    - }
    -
    /* we're trusting the FADT (see above) */
    if (!acpi_gbl_FADT.century)
    /* If we're not trusting the FADT, we should at least make it
    @@ -153,6 +150,20 @@
    else
    yr += cent * 100;

    + /*
    + * Show correct dates for alarms up to a month into the future.
    + * This solves issues for nearly all situations with the common
    + * 30-day alarm clocks in PC hardware.
    + */
    + if (day < today) {
    + if (mo < 12) {
    + mo += 1;
    + } else {
    + mo = 1;
    + yr += 1;
    + }
    + }
    +
    seq_printf(seq, "%4.4u-", yr);
    (mo > 12) ? seq_puts(seq, "**-") : seq_printf(seq, "%2.2u-", mo);
    (day > 31) ? seq_puts(seq, "** ") : seq_printf(seq, "%2.2u ", day);

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