Re: [RFC PATCH net-next 7/9] net: dsa: microchip: ksz9477: add hardware time stamping support

[Christian Eggers]

On Thursday, 12 November 2020, 16:28:44 CET, Christian Eggers wrote:
> Hi Vladimir,
> 
> On Tuesday, 10 November 2020, 20:32:45 CET, Vladimir Oltean wrote:
> > But something is still wrong if you need to special-case the negative
> > correctionField, it looks like the arithmetic is not done on the correct
> > number of bits, either by the driver or by the hardware.
> 
> I got it! 
I got it not!

While keeping the (negative) correction field works perfect when using
PTP over L2 (what I did the last weeks), this causes an unwanted side effect
when using UDP:

...
> User Datagram Protocol, Src Port: 319, Dst Port: 319
> 
>     Source Port: 319
>     Destination Port: 319
>     Length: 62
>  
>  Checksum: 0x2285 incorrect, should be 0x2286 (maybe caused by "UDP checksum offload"?)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

>     [Checksum Status: Bad]
>     [Stream index: 0]
>     [Timestamps]
> 
> Precision Time Protocol (IEEE1588)
> 
>     0000 .... = transportSpecific: 0x0
>     .... 0011 = messageId: Peer_Delay_Resp Message (0x3)
>     0000 .... = Reserved: 0
>     .... 0010 = versionPTP: 2
>     messageLength: 54
>     subdomainNumber: 0
>     Reserved: 0
>     flags: 0x0000
>     correction: 5579788,000000 nanoseconds
>     Reserved: 0
>     ClockIdentity: 0x849000fffe0980f7
>     SourcePortID: 1
>     sequenceId: 785
>     control: Other Message (5)
>     logMessagePeriod: 127
>     requestreceiptTimestamp (seconds): 0
>     requestreceiptTimestamp (nanoseconds): 0
>     requestingSourcePortIdentity: 0x849000fffe0980f6
>     requestingSourcePortId: 2
While correction field is ok (residential delay ~5ms, using one printk...),
the UDP checksum is off by one in all PDelay_Resp messages.

The KSZ device offers on option to set the UDP checksum to zero, but this also
didn't help and additionally wouldn't work for IPv6.

It seems that I should return to "moving T2 from the correction field to the
tail tag" on tx.
 
regards
Christian