Hi Greg, Rob, On 7/26/19 7:32 AM, Greg Kroah-Hartman wrote: > On Thu, Jul 25, 2019 at 02:04:23PM -0700, Frank Rowand wrote: >> On 7/25/19 6:42 AM, Greg Kroah-Hartman wrote: >>> On Tue, Jul 23, 2019 at 05:10:53PM -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. >>>> >>>> v1 -> v2: >>>> - Drop patch to speed up of_find_device_by_node() >>>> - Drop depends-on property and use existing bindings >>>> >>>> v2 -> v3: >>>> - Refactor the code to have driver core initiate the linking of devs >>>> - Have driver core link consumers to supplier before it's probed >>>> - Add support for drivers to edit the device links before probing >>>> >>>> v3 -> v4: >>>> - Tested edit_links() on system with cyclic dependency. Works. >>>> - Added some checks to make sure device link isn't attempted from >>>> parent device node to child device node. >>>> - Added way to pause/resume sync_state callbacks across >>>> of_platform_populate(). >>>> - Recursively parse DT node to create device links from parent to >>>> suppliers of parent and all child nodes. >>>> >>>> v4 -> v5: >>>> - Fixed copy-pasta bugs with linked list handling >>>> - Walk up the phandle reference till I find an actual device (needed >>>> for regulators to work) >>>> - Added support for linking devices from regulator DT bindings >>>> - Tested the whole series again to make sure cyclic dependencies are >>>> broken with edit_links() and regulator links are created properly. >>>> >>>> v5 -> v6: >>>> - Split, squashed and reordered some of the patches. >>>> - Refactored the device linking code to follow the same code pattern for >>>> any property. >>>> >>>> v6 -> v7: >>>> - No functional changes. >>>> - Renamed i to index >>>> - Added comment to clarify not having to check property name for every >>>> index >>>> - Added "matched" variable to clarify code. No functional change. >>>> - Added comments to include/linux/device.h for add_links() >>>> >>>> I've also not updated this patch series to handle the new patch [1] from >>>> Rafael. Will do that once this patch series is close to being Acked. >>>> >>>> [1] - https://lore.kernel.org/lkml/3121545.4lOhFoIcdQ@kreacher/ >>> >>> >>> This looks sane to me. Anyone have any objections for me queueing this >>> up for my tree to get into linux-next now? >> >> I would like for the series to get into linux-next sooner than later, >> and spend some time there. > > Ok, care to give me an ack for it? :) Rob opined to me that if you apply the series, it will go into 5.4 unless reverted. That is also what I would expect. I'm going through the series carefully now. This is currently my highest priority task. I don't yet know if my comments will be minor, or whether I will have larger changes to request. So I am not ready to ack the series yet. -Frank > > thanks, > > greg k-h >
