Re: [RFC][PATCH] Enable async suspend/resume of i2c devices

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

Hi Mark,

On Thu, 7 Apr 2011 07:31:24 +0900, Mark Brown wrote:
> On Wed, Apr 06, 2011 at 10:49:17AM -0400, Alan Stern wrote:
> 
> > Neither is the case.  For these subsystems, the PM dependencies _are_ 
> > known.
> 
> ...
> 
> > Now, I have no idea what the situation is with regard to I2C...
> 
> You definitely don't know *anything* about the relationships for I2C,
> especially in embedded systems.

Can you please elaborate? The i2c subsystem uses a standard
parent-children relationship. It seems fairly similar to USB for
example. The only special case I can think of is with bus multiplexing,
but it would be easy enough to switch off async suspend/resume in this
case.

Sonny, I would expect you to obtain the time saving by only switching
the i2c client device to async suspend/resume. wasn't it the case? i2c
bus device suspend/resume shouldn't matter, as the operation should be
handled by the hardware (e.g. PCI) layer.

Rafael, what happens if a parent is set to async suspend/resume but its
children aren't? Does it disable async altogether for the whole branch,
or does it mean that the branch is processed asynchronously as a whole
but its internal processing is serialized? Or something else?

-- 
Jean Delvare