Re: [Linuxptp-users] Question about hardware receive filter mode

[Keller, J. E <jac...@in...>]

On Thu, 2013-12-19 at 09:16 +0000, Ledda William EXT wrote:
> Hi all, 
> 
> I was querying timestamp capabilities of an interface with ethtool -T
> and I found the following
> 
>  
> 
> Hardware Receive Filter Modes:
> 
>                 none                  (HWTSTAMP_FILTER_NONE)
> 
>                 all                   (HWTSTAMP_FILTER_ALL)
> 
>                 ptpv1-l4-sync         (HWTSTAMP_FILTER_PTP_V1_L4_SYNC)
> 
>                 ptpv1-l4-delay-req    (HWTSTAMP_FILTER_PTP_V1_L4_DELAY_REQ)
> 
>                 ptpv2-l4-sync         (HWTSTAMP_FILTER_PTP_V2_L4_SYNC)
> 
>                 ptpv2-l4-delay-req    (HWTSTAMP_FILTER_PTP_V2_L4_DELAY_REQ)
> 
>                 ptpv2-l2-sync         (HWTSTAMP_FILTER_PTP_V2_L2_SYNC)
> 
>                 ptpv2-l2-delay-req    (HWTSTAMP_FILTER_PTP_V2_L2_DELAY_REQ)
> 
>                 ptpv2-event           (HWTSTAMP_FILTER_PTP_V2_EVENT)
> 
>                 ptpv2-sync            (HWTSTAMP_FILTER_PTP_V2_SYNC)
> 
>                 ptpv2-delay-req       (HWTSTAMP_FILTER_PTP_V2_DELAY_REQ)
> 
>  
> 

The above filters are just all the available ones. The 'good' filter is
ptpv2-event and all. The peer delay and request filters aren't even
listed here! (You can see how old and crummy the hwtstamp_ioctl
interface is....)

Essentially you only need ptpv2-event to support timestamping the
correct list. If you're in slave only mode you need to be able to
timestamp only sync (and peer messages in P2P mode). But having extra
filters doesn't really buy anything as if you can timestamp ptpv2-event
packets you can timestamp any packet needed by ptp4l.

The other filters are available as historically the interface supported
them, even if it wasn't really useful.

Regards,
Jake

> 
>  
> 
> I’m curios to understand the meaning of the different filters in
> particular those related to PTP. Can I found some benefit from  them?
> I mean… if an interface with those filter is “better” than one that
> doesn’t has them?
> 
>  

As long as the interface has ptpv2-event it is consistently more useful
than an interface which does not. However the other filters are not
useful (IMHO).

Ofcourse timestamp all packets is the most useful.

> 
> Thank you 
> 
>  
> 
> William
> 
>  
> 
> 
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