i Greg, On 8/16/19 2:10 AM, Greg Kroah-Hartman wrote: > On Thu, Aug 15, 2019 at 08:09:19PM -0700, Frank Rowand wrote: >> Hi Saravana, >> >> On 8/15/19 6:50 PM, Saravana Kannan wrote: >>> On Fri, Aug 9, 2019 at 10:20 PM Frank Rowand <frowand.list@xxxxxxxxx> wrote: >>>> >>>> On 8/9/19 10:00 PM, Saravana Kannan wrote: >>>>> On Fri, Aug 9, 2019 at 7:57 PM Frank Rowand <frowand.list@xxxxxxxxx> wrote: >>>>>> >>>>>> Hi Saravana, >>>>>> >>>>>> On 7/31/19 3:17 PM, 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() >>>>>>> >>>>>>> v7 -> v8: >>>>>>> - Rebased on top of linux-next to handle device link changes in [1] >>>>>>> >>>>>> >>>>>> >>>>>>> v8 -> v9: >>>>>>> - Fixed kbuild test bot reported errors (docs and const) >>>>>> >>>>>> Some maintainers have strong opinions about whether change logs should be: >>>>>> >>>>>> (1) only in patch 0 >>>>>> (2) only in the specific patches that are changed >>>>>> (3) both in patch 0 and in the specific patches that are changed. >>>>>> >>>>>> I can adapt to any of the three styles. But for style "(1)" please >>>>>> list which specific patch has changed for each item in the change list. >>>>>> >>>>> >>>>> Thanks for the context Frank. I'm okay with (1) or (2) but I'll stick >>>>> with (1) for this series. Didn't realize there were options (2) and >>>>> (3). Since you started reviewing from v7, I'll do that in the future >>>>> updates? Also, I haven't forgotten your emails. Just tied up with >>>>> something else for a few days. I'll get to your emails next week. >>>> >>>> Yes, starting with future updates is fine, no need to redo the v9 >>>> change logs. >>>> >>>> No problem on the timing. I figured you were busy or away from the >>>> internet. >>> >>> I'm replying to your comments on the other 3 patches. Okay with a >>> majority of them. I'll wait for your reply to see where we settle for >>> some of the points before I send out any patches though. >>> >>> For now I'm thinking of sending them as separate clean up patches so >>> that Greg doesn't have to deal with reverts in his "next" branch. We >>> can squash them later if we really need to rip out what's in there and >>> push it again. >>> >>> -Saravana >>> >> >> Please do not do separate clean up patches. The series that Greg has is >> not ready for acceptance and I am going to ask him to revert it as we >> work through the needed changes. >> >> I suspect there will be at least two more versions of the series. The >> first is to get the patches I commented in good shape. Then I will >> look at the patches later in the series to see how they fit into the >> big picture. >> >> In the end, there should be one coherent patch series that implements >> the feature. > > Incremental patches to fix up the comments and documentation is fine, no > need to respin the whole mess. The problem is that the whole thing is a "mess" at this point. I expect the series to go through at least two or three more versions. Please revert the series for now. -Frank > > thanks, > > greg k-h >
