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. -Frank > > thanks, > > greg k-h >
