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. I am _slightly_ more optimistic than Rob that sitting in linux-next for an extended period might reveal any latent issues, so I would like for the series to be in linux-next for an extended period of time. (Yes, my understanding is that Linus does not like patches to be in linux-next if they are not targeted for the next merge window, but I prefer that this patch series spend as much time in linux-next as possible). I have been waiting for the changes to settle down before bringing up the issue of devicetree overlays. Now that the code seems to be settling down, I need to look at how these changes impact overlays. So I do not think the patches will be ready for a Linus pull request until overlays are considered. -Frank > > thanks, > > greg k-h >
