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

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Message-ID: <1157f3fe-f88b-449f-a4c2-aac9d27c95ea@redhat.com>
Date: Mon, 13 Oct 2025 09:45:14 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Marc Kleine-Budde <mkl@...gutronix.de>, netdev@...r.kernel.org,
 Vincent Mailhol <mailhol@...nel.org>
Cc: 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

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?

Thanks,

Paolo