Re: [Linuxptp-devel] Stepping the time backwards with phc2sys

[Richard Cochran]

On Tue, Jan 23, 2018 at 07:38:57AM -0600, Mike Lynch wrote:
> Unless I'm missing something, without rebooting devices A and/or B, how does
> setting the time in the boot scripts for devices A and/or B fix this?

The issue is not the large backwards jump but rather trying to jump
back before 1970, hm?

Thanks,
Richard

--
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
___
Linuxptp-devel mailing list
Linuxptp-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linuxptp-devel

Re: [Linuxptp-devel] Stepping the time backwards with phc2sys

[Mike Lynch]

On 1/22/2018 9:56 PM, Richard Cochran wrote:

On Mon, Jan 15, 2018 at 04:59:13PM +, Loy, Matthias wrote:

we are syncronizing devices using ptp. The absolute time is not
relevant but all devices should be close to each other.

Furthermore devices are connected and disconnected at any time and most
of the time there is no real grandmaster clock with higher priority.

As a result, a new connected device may became ptp grandmaster and all
others adjust there time.

If the new grandmaster is wy back in time, phc2sys refuses to set
the clock. I found the reason in the kernel and created a patch you can
find attached.

What do you think about that? For my understanding it would be okay to
step the realtime clock backwards even below 0 because the value
holding the sceonds is a signed int variable.

I doubt your patch would find acceptance on the lkml.  The check is a
sanity check that makes sense for most use cases.

You can work around this issue by setting some arbitrary date, like
1984, as part of your boot scripts.

Thanks,
Richard

--
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! 
http://atpscan.global.hornetsecurity.com/index.php?atp_str=Xe-YjC9OASLZ0J6-KhBFV2LpYIC_NJr0MMTvDNq4058DtJ6eiEsHK9FWviDmAHe0FYADXT5opOuddfBv9ZTqUZup4VkEU5InRMKtVmOONsxd-SdDJOz8koLkDTPpLVFhsOtHdnMB3PkiB96m_9POZkUy2vnl7UCxmpGYhLXc0JkLGHB80Fr9zCWRtaoJU3AN7toG-rPI-fL0qNL1kE9U0r-M2UwPiAAG_0aejfFIw1HN19k4bsGtikQs5DoVsCedpQfQD8I9LoqyHgG4Xz-7Jhc_KkGBIjIqW4ShXsQUPH32lxYuIzo6IzFkZGFkZTMyYzFkNCM6OiM9qfMAzRxlmQkc0BE-WjLN
___
Linuxptp-devel mailing list
Linuxptp-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linuxptp-devel

I'm not sure how that workaround fixes the issue.  As I understand it 
Mathias' issue is the following:


   Device A PTP synchronized to Device B (time is now)
   Device C comes on line and becomes PTP master (time is way in the past)
   Device A (and probably B) can not set their clocks due to the large
   negative jump.


Unless I'm missing something, without rebooting devices A and/or B, how 
does setting the time in the boot scripts for devices A and/or B fix this?


Mike
--
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot___
Linuxptp-devel mailing list
Linuxptp-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linuxptp-devel

Re: [Linuxptp-devel] Stepping the time backwards with phc2sys

[Richard Cochran]

On Mon, Jan 15, 2018 at 04:59:13PM +, Loy, Matthias wrote:
> we are syncronizing devices using ptp. The absolute time is not
> relevant but all devices should be close to each other.
> 
> Furthermore devices are connected and disconnected at any time and most
> of the time there is no real grandmaster clock with higher priority.
> 
> As a result, a new connected device may became ptp grandmaster and all
> others adjust there time.
> 
> If the new grandmaster is wy back in time, phc2sys refuses to set
> the clock. I found the reason in the kernel and created a patch you can
> find attached.
> 
> What do you think about that? For my understanding it would be okay to
> step the realtime clock backwards even below 0 because the value
> holding the sceonds is a signed int variable.

I doubt your patch would find acceptance on the lkml.  The check is a
sanity check that makes sense for most use cases.

You can work around this issue by setting some arbitrary date, like
1984, as part of your boot scripts.

Thanks,
Richard

--
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
___
Linuxptp-devel mailing list
Linuxptp-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linuxptp-devel

[Linuxptp-devel] Stepping the time backwards with phc2sys

[Loy, Matthias]

Hello,

we are syncronizing devices using ptp. The absolute time is not
relevant but all devices should be close to each other.

Furthermore devices are connected and disconnected at any time and most
of the time there is no real grandmaster clock with higher priority.

As a result, a new connected device may became ptp grandmaster and all
others adjust there time.

If the new grandmaster is wy back in time, phc2sys refuses to set
the clock. I found the reason in the kernel and created a patch you can
find attached.

What do you think about that? For my understanding it would be okay to
step the realtime clock backwards even below 0 because the value
holding the sceonds is a signed int variable.


Best regards,
Matthias

Hottinger Baldwin Messtechnik GmbH, Im Tiefen See 45, 64293 Darmstadt, Germany 
| www.hbm.com

Registered as GmbH (German limited liability corporation) in the commercial 
register at the local court of Darmstadt, HRB 1147
Company domiciled in Darmstadt | Managing Director: Andreas Huellhorst | 
Chairman of the board: Eoghan O�Lionaird

Als Gesellschaft mit beschraenkter Haftung eingetragen im Handelsregister des 
Amtsgerichts Darmstadt unter HRB 1147
Sitz der Gesellschaft: Darmstadt | Geschaeftsfuehrung: Andreas Huellhorst | 
Aufsichtsratsvorsitzender: Eoghan O�Lionaird

The information in this email is confidential. It is intended solely for the 
addressee. If you are not the intended recipient, please let me know and delete 
this email.

Die in dieser E-Mail enthaltene Information ist vertraulich und lediglich fuer 
den Empfaenger bestimmt. Sollten Sie nicht der eigentliche Empfaenger sein, 
informieren Sie mich bitte kurz und loeschen diese E-Mail.
From 7de00c7bfb577964ec04ba4e25d1fe686116ff40 Mon Sep 17 00:00:00 2001
From: Matthias Loy 
Date: Sat, 13 Jan 2018 17:14:26 +0100
Subject: [PATCH] timekeeping-allow-jump-backwards-or-with-zero-distance

---
 kernel/time/timekeeping.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 5018482..a49eb1f 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1274,9 +1274,9 @@ int timekeeping_inject_offset(struct timespec *ts)
 	timekeeping_forward_now(tk);
 
 	/* Make sure the proposed value is valid */
+	/* HBM: Allow to go backward in time or setting the same value */
 	tmp = timespec64_add(tk_xtime(tk),  ts64);
-	if (timespec64_compare(>wall_to_monotonic, ) > 0 ||
-	!timespec64_valid_strict()) {
+	if (!timespec64_valid_strict()) {
 		ret = -EINVAL;
 		goto error;
 	}
-- 
2.14.1

--
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot___
Linuxptp-devel mailing list
Linuxptp-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linuxptp-devel