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

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

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On 05/08/2012 07:38 PM, Oliver Hartkopp wrote:
> 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?

In the current implementation you can register a callback via
platform_data to enable/disable the transceiver. It's up to the board to
do something useful with it.

I think for now I'll take Eric's patch as it is, until we've implemented
something more complicated to support automotive style transceivers :)

Marc

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