On Wed, Aug 07, 2019 at 07:13:26PM -0700, Frank Rowand wrote: > 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. Based on the further comments on this series, and the in-person we had at ELC, I have now reverted these, and the follow-on fixes for this series from my tree, with the hope that an updated patch set will be sent for review soon. thanks, greg k-h
