On Thu, Aug 01, 2019 at 12:59:25PM -0700, Frank Rowand wrote: > On 8/1/19 12:32 PM, Greg Kroah-Hartman wrote: > > On Thu, Aug 01, 2019 at 12:28:13PM -0700, Frank Rowand wrote: > >> Hi Greg, > >> > >> On 7/31/19 11:12 PM, Greg Kroah-Hartman wrote: > >>> On Wed, Jul 31, 2019 at 03:17:13PM -0700, Saravana Kannan wrote: > >>>> Add device-links to track functional dependencies between devices > >>>> after they are created (but before they are probed) by looking at > >>>> their common DT bindings like clocks, interconnects, etc. > >>>> > >>>> Having functional dependencies automatically added before the devices > >>>> are probed, provides the following benefits: > >>>> > >>>> - Optimizes device probe order and avoids the useless work of > >>>> attempting probes of devices that will not probe successfully > >>>> (because their suppliers aren't present or haven't probed yet). > >>>> > >>>> For example, in a commonly available mobile SoC, registering just > >>>> one consumer device's driver at an initcall level earlier than the > >>>> supplier device's driver causes 11 failed probe attempts before the > >>>> consumer device probes successfully. This was with a kernel with all > >>>> the drivers statically compiled in. This problem gets a lot worse if > >>>> all the drivers are loaded as modules without direct symbol > >>>> dependencies. > >>>> > >>>> - Supplier devices like clock providers, interconnect providers, etc > >>>> need to keep the resources they provide active and at a particular > >>>> state(s) during boot up even if their current set of consumers don't > >>>> request the resource to be active. This is because the rest of the > >>>> consumers might not have probed yet and turning off the resource > >>>> before all the consumers have probed could lead to a hang or > >>>> undesired user experience. > >>>> > >>>> Some frameworks (Eg: regulator) handle this today by turning off > >>>> "unused" resources at late_initcall_sync and hoping all the devices > >>>> have probed by then. This is not a valid assumption for systems with > >>>> loadable modules. Other frameworks (Eg: clock) just don't handle > >>>> this due to the lack of a clear signal for when they can turn off > >>>> resources. This leads to downstream hacks to handle cases like this > >>>> that can easily be solved in the upstream kernel. > >>>> > >>>> By linking devices before they are probed, we give suppliers a clear > >>>> count of the number of dependent consumers. Once all of the > >>>> consumers are active, the suppliers can turn off the unused > >>>> resources without making assumptions about the number of consumers. > >>>> > >>>> By default we just add device-links to track "driver presence" (probe > >>>> succeeded) of the supplier device. If any other functionality provided > >>>> by device-links are needed, it is left to the consumer/supplier > >>>> devices to change the link when they probe. > >>> > >>> All now queued up in my driver-core-testing branch, and if 0-day is > >>> happy with this, will move it to my "real" driver-core-next branch in a > >>> day or so to get included in linux-next. > >> > >> I have been slow in getting my review out. > >> > >> This patch series is not yet ready for sending to Linus, so if putting > >> this in linux-next implies that it will be in your next pull request > >> to Linus, please do not put it in linux-next. > > > > It means that it will be in my pull request for 5.4-rc1, many many > > waeeks away from now. > > If you are willing to revert the series before the pull request _if_ I > have significant review issues in the next couple of days, then I am happy > to see the patches get exposure in linux-next. If you have significant review issues, yes, I will be glad to revert them. thanks, greg k-h
