linux-kernel - Questions on rtc drivers...

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Date:	Thu, 21 Feb 2008 01:07:58 +0100
From:	"J.A. Magallón" <jamagallon@....com>
To:	"Linux-Kernel, " <linux-kernel@...r.kernel.org>
Subject: Questions on rtc drivers...

Hi all...

since some time ago I have noticed that mplayer can't use the RTC for
time accounting. Perhaps it is deprecated and should be migrated to
hrtimers, that is what every reference I found said, but the fact is
that nowadays it uses it.

I thought I was because a misbuild of my kernel, but now I have just
built a 2.6.24.2 with every rtc modular to test them (in my case,
just rtc, genrtc and rtc-cmos - I'm not aware of any other that can
work on my mobo, ICH5/i875P).

I use a trimmed down version of the test in Documentacion/rtc.txt.
Results vary:

genrtc fails
crw-r--r-- 1 root root 10, 135 Feb 21 00:53 /dev/rtc
Using /dev/rtc
RTC_IRQP_READ ioctl: Invalid argument

rtc works
crw-r--r-- 1 root root 10, 135 Feb 21 00:53 /dev/rtc
Using /dev/rtc
Initial PI rate: 1024Hz
   2 Hz: ..........
   4 Hz: ..........
   8 Hz: ..........
  16 Hz: ..........
  32 Hz: ..........
  64 Hz: ..........
Device or resource busy
and rtc-cmos behaves strangely. After modprobe, even when /dev/rtc*
are already present, I have to wait even 5 seconds to not have a 'Device or
resource busy' error on open(). And when it opens it just gets stuck
after the first dot:

Using /dev/rtc
Initial PI rate: 1024Hz
   2 Hz: .

The loop is

        for (i=0; i<10; i++)
        {
            res = read(rtc,&data,sizeof(unsigned long));
            if (res<0)
            {
                perror("read");
                exit(errno);
            }
            printf(".");
            fflush(stdout);
        }

They all give different info in /proc/driver/rtc and
/proc/sys/dev/rtc/max-user-freq:

genrtc
crw-r--r-- 1 root root 10, 135 Feb 21 01:03 /dev/rtc
rtc_time    : 00:03:25
rtc_date    : 2008-02-21
rtc_epoch   : 1900
alarm       : 00:00:00
DST_enable  : no
BCD     : yes
24hr        : yes
square_wave : no
alarm_IRQ   : no
update_IRQ  : no
periodic_IRQ    : no
periodic_freq   : 0
batt_status : okay
cat: /proc/sys/dev/rtc/max-user-freq: No such file or directory

rtc
crw-r--r-- 1 root root 10, 135 Feb 21 01:03 /dev/rtc
rtc_time    : 00:03:26
rtc_date    : 2008-02-21
rtc_epoch   : 1900
alarm       : **:00:10
DST_enable  : no
BCD     : yes
24hr        : yes
square_wave : no
alarm_IRQ   : no
update_IRQ  : no
periodic_IRQ    : no
periodic_freq   : 1024
batt_status : okay
64

rtc-cmos
lrwxrwxrwx 1 root root      4 Feb 21 01:03 /dev/rtc -> rtc0
crw-r--r-- 1 root root 254, 0 Feb 21 01:03 /dev/rtc0
rtc_time    : 00:03:39
rtc_date    : 2008-02-21
alrm_time   : **:00:10
alrm_date   : ****-**-**
alarm_IRQ   : no
alrm_pending    : no
24hr        : yes
periodic_IRQ    : no
update_IRQ  : yes
DST_enable  : no
periodic_freq   : 1024
batt_status : okay
cat: /proc/sys/dev/rtc/max-user-freq: No such file or directory

So all of them are not completely interchangeable, the only one that works
as expected is 'rtc'.

What am I doing wrong ? Or is it a bug ?

-- 
J.A. Magallon <jamagallon()ono!com>     \               Software is like sex:
                                         \         It's better when it's free
Mandriva Linux release 2008.1 (Cooker) for i586
Linux 2.6.23-jam05 (gcc 4.2.2 20071128 (4.2.2-2mdv2008.1)) SMP PREEMPT
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