From: Kurt Van Dijck <dev.kurt@vandijck-laurijssen.be>
To: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Zhang Changzhong <zhangchangzhong@huawei.com>,
Maxime Jayat <maxime.jayat@mobile-devices.fr>,
Robin van der Gracht <robin@protonic.nl>,
linux-kernel@vger.kernel.org,
Oleksij Rempel <linux@rempel-privat.de>,
netdev@vger.kernel.org, Marc Kleine-Budde <mkl@pengutronix.de>,
kernel@pengutronix.de, Oliver Hartkopp <socketcan@hartkopp.net>,
Jakub Kicinski <kuba@kernel.org>,
linux-can@vger.kernel.org,
"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH net] can: j1939: j1939_xtp_rx_dat_one(): cancel session if receive TP.DT with error length
Date: Mon, 11 Oct 2021 09:18:42 +0200 [thread overview]
Message-ID: <20211011071842.GA22069@x1.vandijck-laurijssen.be> (raw)
In-Reply-To: <20211011063507.GI29653@pengutronix.de>
On Mon, 11 Oct 2021 08:35:07 +0200, Oleksij Rempel wrote:
> On Sat, Oct 09, 2021 at 04:43:56PM +0800, Zhang Changzhong wrote:
> > On 2021/10/8 19:00, Oleksij Rempel wrote:
> > > On Fri, Oct 08, 2021 at 05:22:12PM +0800, Zhang Changzhong wrote:
> > >> Hi Kurt,
> > >> Sorry for the late reply.
> > >>
> > >> On 2021/9/30 15:42, Kurt Van Dijck wrote:
> > >>> On Thu, 30 Sep 2021 11:33:20 +0800, Zhang Changzhong wrote:
> > >>>> According to SAE-J1939-21, the data length of TP.DT must be 8 bytes, so
> > >>>> cancel session when receive unexpected TP.DT message.
> > >>>
> > >>> SAE-j1939-21 indeed says that all TP.DT must be 8 bytes.
> > >>> However, the last TP.DT may contain up to 6 stuff bytes, which have no meaning.
> > >>> If I remember well, they are even not 'reserved'.
> > >>
> > >> Agree, these bytes are meaningless for last TP.DT.
> > >>
> > >>>
> > >>>>
[...]
> > >>>
> > >>> I think this is a situation of
> > >>> "be strict on what you send, be tolerant on what you receive".
> > >>>
> > >>> Did you find a technical reason to abort a session because the last frame didn't
> > >>> bring overhead that you don't use?
> > >>
> > >> No technical reason. The only reason is that SAE-J1939-82 requires responder
> > >> to abort session if any TP.DT less than 8 bytes (section A.3.4, Row 7).
> > >
> > > Do you mean: "BAM Transport: Ensure DUT discards BAM transport when
> > > TP.DT data packets are not correct size" ... "Verify DUT discards the
> > > BAM transport if any TP.DT data packet has less than 8 bytes"?
> >
> > Yes.
>
> OK, then I have some problems to understand this part:
> - 5.10.2.4 Connection Closure
> The “connection abort” message is not allowed to be used by responders in the
> case of a global destination (i.e. BAM).
>
> My assumption would be: In case of broadcast transfer, multiple MCU are
> receivers. If one of MCU was not able to get complete TP.DT, it should
> not abort BAM for all.
There is indeed no action defined to abort at BAM.
>
> So, "DUT discards the BAM transport" sounds for me as local action.
> Complete TP would be dropped locally.
exact.
Kurt
next prev parent reply other threads:[~2021-10-11 7:18 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-30 3:33 [PATCH net] can: j1939: j1939_xtp_rx_dat_one(): cancel session if receive TP.DT with error length Zhang Changzhong
2021-09-30 7:42 ` Kurt Van Dijck
2021-10-08 9:22 ` Zhang Changzhong
2021-10-08 11:00 ` Oleksij Rempel
2021-10-08 17:09 ` Kurt Van Dijck
2021-10-09 9:12 ` Zhang Changzhong
2021-10-09 8:43 ` Zhang Changzhong
2021-10-11 6:35 ` Oleksij Rempel
2021-10-11 7:18 ` Kurt Van Dijck [this message]
2021-10-11 10:40 ` Zhang Changzhong
2021-10-12 10:21 ` Oleksij Rempel
2021-10-12 10:41 ` Kurt Van Dijck
2021-10-12 11:09 ` Oleksij Rempel
2021-10-17 10:32 ` Marc Kleine-Budde
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