On Tuesday, November 04, 2014 10:11:35 AM Ulf Hansson wrote: > On 4 November 2014 02:57, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > > On Monday, November 03, 2014 10:41:02 AM Alan Stern wrote: > >> On Mon, 3 Nov 2014, Russell King - ARM Linux wrote: > >> > >> > That makes it pretty horrid from the point of view of having bus > >> > management code, because we now have the management of the bus clock > >> > split between the bus layer and the device driver. > >> > > >> > This is /really/ a problem for runtime PM. Runtime PM permits there > >> > to be a bus layer involved - and runtime PM can also be coupled up > >> > to PM domains as well. For all this stuff, the context which the > >> > callbacks are called in depends on whether the driver itself has > >> > marked the device as having IRQ-safe callbacks. > >> > > >> > That's fine, but the bus and PM domain level code then /really/ needs > >> > to know what context they're being called in, so they know whether > >> > they can sleep or not, or they must to be written to always use > >> > non-sleeping functions so they work in both contexts. If we assume > >> > the former, then that implies that the irq-safe flag must never change > >> > state between a suspend and a resume. > >> > >> If a bus subsystem or PM domain is going to allow its drivers to choose > >> between IRQ-safe and non-IRQ-safe runtime PM, then it is up to the > >> subsystem to come up with a way for drivers to indicate their choice. > >> > >> I tend to agree with Rafael that testing dev->power.irq_safe should be > >> good enough, with no real need for a wrapper. But the subsystem can > >> use a different mechanism if it wants. > >> > >> Bear in mind, however, that once the irq_safe flag has been set, the > >> runtime PM core offers no way to turn it off again. > > > > There is a problem with it, though. Say, a driver handles a device that > > may or may not be in a power domain. Or in other words, the power domain > > the device is in may or may not be always on. If the domain is always on, > > the runtime PM callbacks are IRQ-safe (they depend on the driver only). > > If it isn't, they may not be IRQ-safe. How's the driver going to decide > > whether or not to set power.irq_safe? > > From my point of view; the decision whether the driver will set the > IRQ safe flag is in principle a software design choice. > > Currently genpd isn't able to power off, if one of its devices are IRQ > safe configured. That's a limitation in genpd which we need to fix and > it's on my TODO list. > > My point is thus, I don't think the driver should care about PM > domains at all regarding using the IRQ safe option. Does that make > sense? Yes, it does, and that's the heart of the problem above. The driver should not care about wherther or not the device is in a power domain, but it needs to know that when deciding whether or not to set power.irq_safe. Catch 22. -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
