On Wednesday, July 02, 2014 10:27:06 AM Alan Stern wrote: > On Wed, 2 Jul 2014, Rafael J. Wysocki wrote: > > > > Then you have no other objections to the patch? > > > > My concern still is that it will be confusing, because people won't read the > > documentation carefully enough and will confuse "runtime PM never used" with > > "hardware can't do PM". I'm not sure how to make that more clear, though. > > I could emphasize that distinction a little more strongly in the > documentation. > > > Also we have the no_callbacks flag and I wonder if/how it is related to the > > new one. Do we still need both? > > They mean different things. The no_callbacks flag is used when we want > the PM core to think the device can be in RPM_SUSPENDED at times (it is > "logically suspended"). rpm_not_supported is used when we want the PM > core to think the device must always be in RPM_ACTIVE. > > > In addition to that, I think that "hardware can't do PM" should apply to the > > handling of system suspend resume too. > > Maybe. For the use case Dan Williams and I are working on, it doesn't > matter; for other cases it might matter. That's why I named the flag > "rpm_not_supported" -- it applies specifically to runtime PM, not > system PM. > > Here's a brief summary of the story behind this patch... > > At one point, I suggested to Dan that instead of doing something > special for these devices, we could simply have the runtime_suspend() > routine always return -EBUSY. He didn't like that idea because then > the user would see the device was never powering down but would have no > idea why. The rpm_not_supported flag provides this information to the > user by causing the power/runtime_status attribute to say "not > supported". (Although to be entirely fair, we could just put a message > in the kernel log during probe if the hardware doesn't support runtime > suspend.) > > Instead, Dan introduced a messy PM QoS mechanism in commit > e3d105055525. I didn't like that approach, but Greg merged it before I > objected. > > Do you have any suggestions?
I need some more time to think about that. I'm on vacation till Monday, I should be able to get to this by then. I hope that's not a problem. Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
