Hi Greg, Saravana, On 8/1/19 11:37 PM, Greg Kroah-Hartman wrote: > 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. Just a heads up that I have sent review issues in reply to version 7 of this patch series. We'll see what the responses are to my review comments, but I am expecting the changes are big enough to result in a new version (or a couple more versions) of the patch series. No rush to revert version 9 since your 5.4-rc1 pull request is still not near, and I am glad for whatever exposure these patches are getting in linux-next. Thanks, Frank > > thanks, > > greg k-h >
