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

[Vincent Mailhol <mailhol@kernel.org>]

Hi Paolo and Simon,

Sorry for the build error.

(for the record, Simon separately reported the same issue here:
 https://lore.kernel.org/linux-can/aOzJZ1NsKxNMvIzJ@horms.kernel.org/)

On 13/10/2025 at 16:45, Paolo Abeni wrote:
> Ni,
> 
> On 10/12/25 4:20 PM, Marc Kleine-Budde wrote:
>> From: Vincent Mailhol <mailhol@kernel.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@kernel.org>
>> Link: https://patch.msgid.link/20251012-can-fd-doc-v1-2-86cc7d130026@kernel.org
>> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.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::
                                                      ^
This is the culprit. There should have been as single colon here...

>> +
>> +- **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 it is:

  https://lore.kernel.org/r/20251013-can-fd-doc-v2-0-5d53bdc8f2ad@kernel.org


Yours sincerely,
Vincent Mailhol