Re: [PATCH v5 4/6] can: introduce the data bitrate configuration for CAN FD

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 02/27/2014 07:05 PM, Oliver Hartkopp wrote:
> On 27.02.2014 09:43, Marc Kleine-Budde wrote:
> 
>>> +		if (priv->do_set_data_bittiming) {
>>> +			/* Finally, set the bit-timing registers */
>>> +			err = priv->do_set_data_bittiming(dev);
>>> +			if (err)
>>> +				return err;
>>> +		}
>>
>> Do we really need the do_set_data_bittiming() callback? Allmost all
>> drivers set the bitrate during open and not asynchronously (when the
>> interface is down) via the set_bittiming() callback. If there is a
>> driver which really needs this callback, we can introduce it.
> 
> No. I assume you did not check the current implementation %-)

Yes, but...no :)

> The bitrate is always set via do_set[_data]_bittiming() when the interface is
> down - and *not* during the open process.

No, not _always_. The flexcan and at91 drivers (maybe others, too) write
the values during open().

> In the open process only the availability of the bitrate(s) is checked before
> the controller is set into operational mode.

Yes, by the framework. This is good.

> It is pretty straight forward to introduce do_set_data_bittiming() as a
> different register set is addressed for CAN FD.

The reason why I don't want to introduce a do_set_data_bittiming() is
that it makes the driver more complicated. If you really want to write
it into the registers, you have to power up you CAN core, as on modern
controllers you cannot write to regs if the clocks are turned off. So
you have to turn on the clock, power up your chip, get into the correct
mode, write the bittiming and power down everything again. During open()
you do the same thing again but don't write the bit timing registers. So
better keep things simple.

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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