Re: [linux-pm] [PATCH] i2c: Use generic subsystem-level power management callbacks

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Sun, 14 Mar 2010, Rafael J. Wysocki wrote:

> On Sunday 14 March 2010, Alan Stern wrote:
> > On Sun, 14 Mar 2010, Rafael J. Wysocki wrote:
> > 
> > > > You know, maybe we should allow bus types to use both the old and new
> > > > interfaces.  It would make life easier for other subsystems in addition
> > > > to i2c.
> > > > 
> > > > This doesn't mean that the core would end up calling two sets of
> > > > suspend routines.  If the bus type uses legacy routines then all the
> > > > non-runtime entries in the pm_ops structure would be empty.
> > > > 
> > > > The changes to the PM core necessary to do this are quite small.
> > > 
> > > Not really.  The detection that the particular callback is not present happens
> > > in pm_op(), while the decision which framework to use is made at the
> > > device_[suspend|resume]() level.
> > 
> > All you have to do is change the "else if" lines in
> > device_[suspend|resume]() to "if".
> 
> Then, if a bus type implements both "new" and "old" callbacks, we'll end up
> calling both.  Not nice.

Why would a bus type implement both?  Or looked at another way, if it 
did implement both then wouldn't it want both sets of callbacks to be 
invoked?

If a bus type does define both types of callback by mistake and only 
wants one of them to be used, that's a bug -- pure and simple.  It's 
not the PM core's fault if something goes wrong under those 
circumstances.

> > Sure.  But suppose you _don't_ want to spend the time implementing new
> > callbacks to replace the existing legacy suspend and resume methods,
> > whereas you _do_ want to implement runtime PM.  Runtime PM forces the
> > bus type to have a pm_ops member,
> 
> Which is very much on purpose, because the legacy suspend and resume have no
> idea about the runtime stuff.
> 
> > which as you point out, will prevent the legacy methods from being called.
> 
> Yes, that's intentional.
> 
> That said, I think we might modify the generic callbacks in generic_ops.c to
> call the drivers' legacy callbacks if the "new" ones are not defined.

That's no good -- the routines in generic_ops.c invoke the _driver's_
callbacks, not the _bus type's_ callbacks.

I suppose you could write a new set of generic "legacy" callbacks that
would work just as though the new ops weren't defined.  Removing those
"else"s would be a lot simpler, though.

Alan Stern

--
To unsubscribe from this list: send the line "unsubscribe linux-i2c" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Linux GPIO]     [Linux SPI]     [Linux Hardward Monitoring]     [LM Sensors]     [Linux USB Devel]     [Linux Media]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux