Re: [PATCH] can: flexcan: add PM support

[Oliver Hartkopp <socketcan@hartkopp.net>]

On 08.05.2012 19:14, Eric Bénard wrote:

> Le Tue, 08 May 2012 17:46:09 +0200,
> Marc Kleine-Budde <mkl@pengutronix.de> a écrit :
> 
>> On 05/08/2012 05:30 PM, Eric Bénard wrote:
>>> Hi Marc,
>>>
>>> Le Tue, 08 May 2012 17:18:34 +0200,
>>> Marc Kleine-Budde <mkl@pengutronix.de> a écrit :
>>>
>>>> On 05/08/2012 05:12 PM, Eric Bénard wrote:
>>>>> tested on an i.MX257
>>>>
>>>> What about the transceiver? Does is make sense to switch it off, too?
>>>>
>>> this could make sense on platform which have a transceiver with an
>>> enable input. I can add flexcan_transceiver_switch after/before
>>> flexcan_chip_disable/enable but won't be able to test that feature.
>>
>> I looked at two ethernet drivers: ethernet/intel/ixgbe/ixgbe_main.c and
>> ethernet/intel/ixgbe/ixgbe_main.c and AFAICS they basically do the same
>> as in open/close. (btw: the flexcan driver switches the transceiver
>> on/off on open/close.) I haven't implemented any network driver pm yet,
>> but what is a driver supposed to do in suspend/resume?
>>
> concerning the transceiver : that depends if you need to resume when
> receiving a message on the CAN bus in which case you can't disable the
> transceiver (btw, I have an other patch which enable wakeup when
> receiving a message on the CAN bus, but I need to clean and test it
> again).


I wonder if you mix up the enabling/disabling of the CAN transceiver (trx)
with the entire system power management.

E.g. if you take the TJA1054A as an example, you can switch the trx into a
mode that switches off the power supply (INH-line) in order to wake up with a
received CAN frame, which switches on the power supply and boots the system.

Even if you don't switch the power supply with the INH pin the trx wakes up
with CAN traffic in this mode.

To me switching the trx modes only makes sense to implement system power
management states. IMO there's no need to switch them when setting the
interface to up/down state. Or did i miss anything?

Regards,
Oliver