netdev - Re: [PATCH net 9/9] can: add Transmitter Delay Compensation (TDC) documentation

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Message-ID: <20251015-electric-cyber-goshawk-19e7fc-mkl@pengutronix.de>
Date: Wed, 15 Oct 2025 11:43:50 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Vincent Mailhol <mailhol@...nel.org>, 
	davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org, 
	kernel@...gutronix.de
Subject: Re: [PATCH net 9/9] can: add Transmitter Delay Compensation (TDC)
 documentation

On 13.10.2025 09:45:14, Paolo Abeni wrote:
> Ni,
> 
> On 10/12/25 4:20 PM, Marc Kleine-Budde wrote:
> > From: Vincent Mailhol <mailhol@...nel.org>
> > 
> > Back in 2021, support for CAN TDC was added to the kernel in series [1]
> > and in iproute2 in series [2]. However, the documentation was never
> > updated.
> > 
> > Add a new sub-section under CAN-FD driver support to document how to
> > configure the TDC using the "ip tool".
> > 
> > [1] add the netlink interface for CAN-FD Transmitter Delay Compensation (TDC)
> > Link: https://lore.kernel.org/all/20210918095637.20108-1-mailhol.vincent@wanadoo.fr/
> > 
> > [2] iplink_can: cleaning, fixes and adding TDC support
> > Link: https://lore.kernel.org/all/20211103164428.692722-1-mailhol.vincent@wanadoo.fr/
> > 
> > Signed-off-by: Vincent Mailhol <mailhol@...nel.org>
> > Link: https://patch.msgid.link/20251012-can-fd-doc-v1-2-86cc7d130026@kernel.org
> > Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
> > ---
> >  Documentation/networking/can.rst | 60 ++++++++++++++++++++++++++++++++
> >  1 file changed, 60 insertions(+)
> > 
> > diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst
> > index ccd321d29a8a..402fefae0c2f 100644
> > --- a/Documentation/networking/can.rst
> > +++ b/Documentation/networking/can.rst
> > @@ -1464,6 +1464,66 @@ Example when 'fd-non-iso on' is added on this switchable CAN FD adapter::
> >     can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
> >  
> >  
> > +Transmitter Delay Compensation
> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +At high bit rates, the propagation delay from the TX pin to the RX pin of
> > +the transceiver might become greater than the actual bit time causing
> > +measurement errors: the RX pin would still be measuring the previous bit.
> > +
> > +The Transmitter Delay Compensation (thereafter, TDC) resolves this problem
> > +by introducing a Secondary Sample Point (SSP) equal to the distance, in
> > +minimum time quantum, from the start of the bit time on the TX pin to the
> > +actual measurement on the RX pin. The SSP is calculated as the sum of two
> > +configurable values: the TDC Value (TDCV) and the TDC offset (TDCO).
> > +
> > +TDC, if supported by the device, can be configured together with CAN-FD
> > +using the ip tool's "tdc-mode" argument as follow::
> > +
> > +- **omitted**: when no "tdc-mode" option is provided, the kernel will
> > +  automatically decide whether TDC should be turned on, in which case it
> 
> The above apparently makes htmldoc unhappy:
> 
> New errors added
> --- /tmp/tmp.ZsYbmUst3Y	2025-10-12 14:23:45.746737362 -0700
> +++ /tmp/tmp.8o1xOCQtDp	2025-10-12 14:58:29.920405220 -0700
> @@ -15,0 +16 @@
> +/home/doc-build/testing/Documentation/networking/can.rst:1484: ERROR:
> Unexpected indentation.
> 
> Could you please address the above and send a v2?

Here you go:

| https://lore.kernel.org/all/20251014122140.990472-1-mkl@pengutronix.de/

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
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