On Wed, 8 Aug 2012, Ming Lei wrote: > On Wed, Aug 8, 2012 at 4:45 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > On Tuesday, August 07, 2012, Ming Lei wrote: > >> On Tue, Aug 7, 2012 at 7:23 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > >> >> Yes, I agree, but I don't think it may make .runtime_post_resume > >> >> not doable, do I? > >> > > >> > No more device PM callbacks, please. > >> > >> IMO, what the patch is doing is to introduce one callback which > >> is just called after .runtime_resume is completed, > > > > No, it is not a callback. It is a function to be run _once_ when the device is > > known to be active. It is not a member of a data type or anything like this. > > Looks it was said by Alan, not me, :-) > > "The documentation should explain that in some ways, "func" is like a > workqueue callback routine:". > > See http://marc.info/?l=linux-usb&m=134426838507799&w=2 I didn't say it _was_ a callback; I said it was _like_ a callback in some ways. > If so, I am wondering why the 'func' can't be called in .runtime_resume > directly, and follow the below inside caller at the same time? > > if (device is active or disabled) > call func(device). That was my original suggestion. Rafael pointed out that having a single function call to do this would make it easier for driver writers to get it right. > > No, not to speed up resume. The idea is to allow drivers to run something > > when the resume is complete, so that they don't have to implement a "resume > > detection" logic or use .runtime_resume() to run things that don't belong > > there. > > Looks it was said by you, :-) > > "Unless your _driver_ callback is actually executed from within a PM domain > callback, for example, and something else may be waiting for it to complete, > so your data processing is adding latencies to some other threads. I'm not > making that up, by the way, that really can happen." > > See http://marc.info/?l=linux-pm&m=134394271517527&w=2 > > Alan also said "Okay, those are valid reasons" for the idea. Except for > this one, I don't see other obvious advantages about the patch. Those _are_ the two advantages: The runtime-resume method does nothing but bring the device back to full power; it doesn't do any other processing; It's easier than calling pm_runtime_get() followed by a test to see whether the device is active. > Suppose one driver may drive 10000 same devices, the same data will be > stored inside all the 10000 device instances, it is a good way to do it? If you've got a system with 10000 device instances, you can probably spare the memory needed to store these function pointers. But you're right that this is a disadvantage. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
