On Mon, Jul 24, 2017 at 10:38:41AM -0400, Alan Stern wrote: > On Mon, 24 Jul 2017, Johan Hovold wrote: > > > Make sure that the controller is runtime resumed when system suspending > > to avoid an external abort when accessing the interrupt registers: > > > > Unhandled fault: external abort on non-linefetch (0x1008) at 0xd025840a > > ... > > [<c05481a4>] (musb_default_readb) from [<c0545abc>] (musb_disable_interrupts+0x84/0xa8) > > [<c0545abc>] (musb_disable_interrupts) from [<c0546b08>] (musb_suspend+0x38/0xb8) > > [<c0546b08>] (musb_suspend) from [<c04a57f8>] (platform_pm_suspend+0x3c/0x64) > > > > This is easily reproduced on a BBB by enabling the peripheral port only > > (as the host port may enable the shared clock) and keeping it > > disconnected so that the controller is runtime suspended. (Well, you > > would also need to the not-yet-merged am33xx-suspend patches by Dave > > Gerlach to be able to suspend the BBB.) > > > > This is a regression that was introduced by commit 1c4d0b4e1806 ("usb: > > musb: Remove pm_runtime_set_irq_safe") which allowed the parent glue > > device to runtime suspend and thereby exposed a couple of older issues: > > > > Register accesses without explicitly making sure the controller is > > runtime resumed during suspend was first introduced by commit > > c338412b5ded ("usb: musb: unconditionally save and restore the context > > on suspend") in 3.14. > > > > Commit a1fc1920aaaa ("usb: musb: core: make sure musb is in RPM_ACTIVE on > > resume") later started setting the RPM status to active during resume > > without first making sure that the parent was runtime resumed. This was > > also implicitly relying on the parent always being active. Since commit > > 71723f95463d ("PM / runtime: print error when activating a child to > > unactive parent") this now also results in following warning: > > > > musb-hdrc musb-hdrc.0: runtime PM trying to activate child device > > musb-hdrc.0 but parent (47401400.usb) is not active > > I don't understand this. Why wouldn't the parent be in RPM_ACTIVE at > this time? After all, how could the system be expected to resume a > child device if its parent wasn't fully active? The parent for a musb controller is a "glue" device (e.g. musb_dsps) which previously was always kept active, but that's no longer the case as mentioned above. In a system with two controllers (e.g. a Beagle Bone Black), the host port may be active and keep the shared clock enabled (managed by the grandparent device). Thereby the external-abort crash can be avoided when suspending a disconnected (and runtime suspended) peripheral port. When the system is later resumed, you would hit that broken activation code of the runtime suspended device, with a likewise runtime suspended parent, and the warning would be printed. > In general, during a system resume callback we should bring a device > back to full power, tell the PM core that this has been done, and leave > it at full power until the whole system resume is finished. For > efficiency we can avoid doing this in cases where the device was in > runtime suspend before the system suspend began, but you have to be > very careful about it -- see the documentation for the ->prepare > callback in Documentation/driver-api/pm/devices.rst. Right, this is how things should have been implemented if it is at all possible too keep the device runtime suspended across system suspend. Thanks, Johan