Messages in this thread | | | Date | Tue, 22 Nov 2011 10:57:58 -0500 (EST) | From | Alan Stern <> | Subject | Re: [PATCH 5] PM: Update comments describing device power management callbacks |
| |
On Mon, 21 Nov 2011, Rafael J. Wysocki wrote:
> On Monday, November 21, 2011, Alan Stern wrote: > > On Mon, 21 Nov 2011, Rafael J. Wysocki wrote: > > > > > > > I said "Analogous to @suspend()" instead. I'm not sure why this is not > > > > > sufficient? > > > > > > > > Because @suspend() is very different! Its description basically says > > > > to do three things: > > > > > > > > Quiesce the device, > > > > > > > > Put it into a low-power state, > > > > > > > > And enable wakeup events. > > > > > > No, it doesn't any more. It's being changed by the proposed patch too. :-) > > > > I must have missed reading that part. Okay... but it seems weird that > > none of the new descriptions says anything about changing the power > > state. Shouldn't the description of @suspend say something like "For > > many platforms and subsystems, the device should be put in a low-power > > state"? > > Hmm. I'm not really sure, actually, because I'd recommend that subsystems > rather than drivers change power states of devices and this description > is targeted at driver writers mostly.
The same data structure (dev_pm_ops) is used for both drivers and subsystems. Therefore the comments should be directed toward both driver writers and subsystem writers.
You could say: "For many platforms, the subsystem @suspend() or @suspend_noirq() callback should put the device in a low-power state. Some subsystems may require the driver to do this instead."
> > > > @freeze() is supposed to do the first but not the second or third. > > > > This makes it only 33% similar to @suspend(). :-) > > > > > > > > Also, the description of @suspend() says nothing about having a > > > > consistent memory image. > > > > > > Because that is irrelevant. The state of the device after the resume > > > has to be consistent, regardless of whether the resume is from RAM or > > > from an on-disk image. > > > > Sure, the device's state will be consistent. But will the contents of > > memory image be consistent? Not if the device was doing DMA writes > > during the time when the image was created. > > Well, since .suspend() is also expected to stop DMA, that's rather moot.
It won't be moot if you add the sentences I recommend above. You could add an additional sentence: "Either way, the @freeze() and @freeze_noirq() callbacks (both the subsystem's and the driver's) should always avoid changing the device's state."
Alan Stern
| |