# Re: \[PATCH v5 2/7\] can: bittiming: allow TDC{V,O} to be zero and add can\_tdc\_const::tdc{v,o,f}\_min

- From: Marc Kleine-Budde \<mkl@pengutronix.de\>
- Date: 2021-08-17 20:01:32 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/08/1480792
- Thread: https://ratatoskr.run/linux-can/2021/08/1478077/t.md

```text
On 17.08.2021 00:49:35, Vincent MAILHOL wrote:
> > We have 4 operations:
> > - tdc-mode off                  switch off tdc altogether
> > - tdc-mode manual tdco X tdcv Y configure X and Y for tdco and tdcv
> > - tdc-mode auto tdco X          configure X tdco and
> >                                 controller measures tdcv automatically
> > - /* nothing */                 configure default value for tdco
> >                                 controller measures tdcv automatically
> 
> The "nothing" does one more thing: it decides whether TDC should
> be activated or not.
> 
> > The /* nothing */ operation is what the old "ip" tool does, so we're
> > backwards compatible here (using the old "ip" tool on an updated
> > kernel/driver).
> 
> That's true but this isn't the real intent. By doing this design,
> I wanted the user to be able to transparently use TDC while
> continuing to use the exact same ip commands she or he is used
> to using.

Backwards compatibility using an old ip tool on a new kernel/driver must
work. In case of the mcp251xfd the tdc mode must be activated and tdcv
set to the automatic calculated value and tdco automatically measured.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |
```

## Attachments

- [signature.asc](https://ratatoskr.run/netdev/2021/08/1480792/attachment/0) (application/pgp-signature, 488 bytes)