linux-kernel - RTC seems broken on 2.6.38-rc1 for RTCs lacking alarms.

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Message-ID: <4D38A051.2010301@caviumnetworks.com>
Date:	Thu, 20 Jan 2011 12:51:29 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	John Stultz <john.stultz@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: RTC seems broken on 2.6.38-rc1 for RTCs lacking alarms.

The hwclock program on my MIPS Debian GNU/Linux 5.0 system quit
working with 2.6.38-rc1.

This particular ds1307 has no interrupt connection, so the alarm
feature cannot be used.  Because of this the
rtc_class_ops.set_alarm() function always will return -EINVAL


This problem appears to be related to commits:
042620a RTC: Remove UIE emulation
6610e08 RTC: Rework RTC code to use timerqueue for events

My system uses a ds1307 RTC which still works as evidenced by the
kernel boot messages.

.
.
.
rtc-ds1307 0-0068: setting system clock to 2011-01-20 19:58:48 UTC 
(1295553528)
.
.
.

But hwclock now fails here is some nice strace output:
.
.
.
open("/dev/rtc0", O_RDONLY|O_LARGEFILE) = 3
ioctl(3, PRESTO_GETMOUNT or RTC_UIE_ON, 0) = 0
_newselect(4, [3], NULL, NULL, {5, 0})  = 0 (Timeout)
write(2, "select() to /dev/rtc0 to wait for"..., 55select() to /dev/rtc0 
to wait for clock tick timed out
) = 55
ioctl(3, PRESTO_SETPID or RTC_UIE_OFF, 0) = 0
close(3)                                = 0
exit_group(1)                           = ?


The hwclock program is asking to put the clock in UIE mode and then
does a select() on it.  Since the alarm doesn't work, the select times out.

Previously the ioctl(RTC_UIE_ON) would return EINVAL:
.
.
.
open("/dev/rtc0", O_RDONLY|O_LARGEFILE)  = 3
ioctl(3, PRESTO_GETMOUNT or RTC_UIE_ON, 0) = -1 EINVAL (Invalid argument)
ioctl(3, PRESTO_SETOPT or RTC_RD_TIME, {tm_sec=48, tm_min=41, 
tm_hour=20, tm_mday=20, tm_mon=0, tm_year=111, ...}) = 0
ioctl(3, PRESTO_SETOPT or RTC_RD_TIME, {tm_sec=48, tm_min=41, 
tm_hour=20, tm_mday=20, tm_mon=0, tm_year=111, ...}) = 0
.
.
.

The problem seems to be that rtc_update_irq_enable() no longer returns
-EINVAL when it cannot set the alarm.

David Daney
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