linux-kernel - Re: PATCH: /proc/acpi/alarm: handle day-of-month wraparound on readback

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Date:	Mon, 01 Dec 2008 12:02:06 -0500
From:	Mark Lord <lkml@....ca>
To:	Len Brown <lenb@...nel.org>,
	Alessandro Zummo <a.zummo@...ertech.it>
Cc:	David Brownell <david-b@...bell.net>,
	lkml <linux-kernel@...r.kernel.org>, rtc-linux@...glegroups.com,
	linux-acpi@...r.kernel.org
Subject: Re: PATCH: /proc/acpi/alarm: handle day-of-month wraparound on readback

Mark Lord wrote:
> 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).
..

I should add, that the above test requires that the alarm
be set for any day of the *next* month from the current month.
My MythTV box does a readback test any time it programs a wakeup,
and noticed the bug over this past weekend (2008-11-30).

> 
> 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@...ox.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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