netdev - Re: [PATCH net-next v3 0/6] ptp: Support hardware clocks with additional free running cycle counter

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20220504085552.3ff84d0c@kernel.org>
Date:   Wed, 4 May 2022 08:55:52 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
Cc:     richardcochran@...il.com, vinicius.gomes@...el.com,
        yangbo.lu@....com, davem@...emloft.net, mlichvar@...hat.com,
        netdev@...r.kernel.org, Willem de Bruijn <willemb@...gle.com>,
        Martin KaFai Lau <kafai@...com>,
        Jonathan Lemon <jonathan.lemon@...il.com>
Subject: Re: [PATCH net-next v3 0/6] ptp: Support hardware clocks with
 additional free running cycle counter

On Sun,  1 May 2022 13:18:30 +0200 Gerhard Engleder wrote:
> ptp vclocks require a clock with free running time for the timecounter.
> Currently only a physical clock forced to free running is supported.
> If vclocks are used, then the physical clock cannot be synchronized
> anymore. The synchronized time is not available in hardware in this
> case. As a result, timed transmission with TAPRIO hardware support
> is not possible anymore.
> 
> If hardware would support a free running time additionally to the
> physical clock, then the physical clock does not need to be forced to
> free running. Thus, the physical clocks can still be synchronized while
> vclocks are in use.
> 
> The physical clock could be used to synchronize the time domain of the
> TSN network and trigger TAPRIO. In parallel vclocks can be used to
> synchronize other time domains.
> 
> One year ago I thought for two time domains within a TSN network also
> two physical clocks are required. This would lead to new kernel
> interfaces for asking for the second clock, ... . But actually for a
> time triggered system like TSN there can be only one time domain that
> controls the system itself. All other time domains belong to other
> layers, but not to the time triggered system itself. So other time
> domains can be based on a free running counter if similar mechanisms
> like 2 step synchroisation are used.
> 
> Synchronisation was tested with two time domains between two directly
> connected hosts. Each host run two ptp4l instances, the first used the
> physical clock and the second used the virtual clock. I used my FPGA
> based network controller as network device. ptp4l was used in
> combination with the virtual clock support patches from Miroslav
> Lichvar.

The netdev parts looks sane, I think.

Richard? Let me also add Willem, Jonathan and Martin.