On 4 November 2014 14:59, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > 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. Why is it catch22? The problem is supposed to be fixed in the generic PM domain. How we do that is a different question. Until genpd get fixed, the driver can still keep using irq_safe if they want to. It will only lead to limitations if the device is attached to a genpd. Kind regards Uffe -- 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
