Message ID | 20190904211126.47518-1-saravanak@google.com |
---|---|
Headers | show |
Series | Solve postboot supplier cleanup and optimize probe ordering | expand |
Quoting Saravana Kannan (2019-09-04 14:11:19) > v10->v11: > - Dropped 6/7 and 7/7 from previous series that tried to handle cycles in DT > dependencies. We can solve it later when we actually hit a real world issue > in DT. > - Added a new 1/7 that shifts the numbering for the rest of the patches > - 1/7 adds a way to look up a device from a fwnode so that this series can work > across bus and firmware types > - 3/7 removed references to platform_device from of/property.c > - 4/7 Minor variable rename > - 4/7 Defer sync_state() be default at driver core level and resume at > late_initcall_sync(). That way, we don't depend on any specific bus types > having to pause/resume sync_state() till late_initcall_sync() Please reverse this list so that most recent series changes come first and we don't have to scroll through all the history to get to what has changed recently. Also, please Cc me on future changes and I would suggest involving any subsystem maintainers that this code is optimizing for. Looks like Mark Brown and Georgi Djakov should be included in this series for awareness (but it's at v11 already!)
On Wed, Sep 04, 2019 at 02:11:19PM -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. Hearing no real complaints again, I've now queued these up in my tree. thanks, greg k-h