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? :) thanks, greg k-h
