linux-kernel - Re: platform/i2c busses: pm runtime and system sleep

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Message-ID: <20101218132029.GA22273@opensource.wolfsonmicro.com>
Date:	Sat, 18 Dec 2010 13:20:29 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Rabin Vincent <rabin@....in>, stern@...land.harvard.edu,
	linux-pm@...ts.linux-foundation.org, linux-i2c@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: platform/i2c busses: pm runtime and system sleep

On Sat, Dec 18, 2010 at 01:54:57PM +0100, Rafael J. Wysocki wrote:
> On Saturday, December 18, 2010, Mark Brown wrote:

> > SPI and platform (the first two buses I looked at) both seem to have
> > legacy suspend operations too?  Clearly the bus would need to provide an
> > op to invoke the legacy call but the logic which prioritises the pm_ops
> > over the legacy operation is generic.

> Well, the problem with that is the driver would need to tell the generic call
> what the legacy routine is and there's no, er, generic way to do that.

> In the i2c case, for example, there is struct i2c_driver that contains the
> ->suspend() and ->resume() pointers, so the bus type driver _knows_ how to
> get there, but the PM core doesn't have this information.

Sure, but this could be readily accomplished by providing bus
legacy_suspend() and legacy_resume() operations that the generic code
could use to do the actual call.  This would save them all implmeneting
essentially the same decision making code for all the various different 
PM operations - the only bit that differs between buses is going to be
the actual process for calling the legacy API.

Like I say, I'm not sure if it's actually worth it.
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