netdev - Re: [PATCH v5 2/7] can: bittiming: allow TDC{V,O} to be zero and add can_tdc_const::tdc{v,o,f}

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Message-ID: <20210817200123.4wcdwsdfsdjr3ovk@pengutronix.de>
Date:   Tue, 17 Aug 2021 22:01:23 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Vincent MAILHOL <mailhol.vincent@...adoo.fr>
Cc:     linux-can <linux-can@...r.kernel.org>,
        Stefan Mätje <Stefan.Maetje@....eu>,
        netdev <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/7] can: bittiming: allow TDC{V,O} to be zero and add
 can_tdc_const::tdc{v,o,f}_min

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           |
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