Hi Greg, On 7/31/19 11:12 PM, Greg Kroah-Hartman wrote: > On Wed, Jul 31, 2019 at 03:17:13PM -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. > > All now queued up in my driver-core-testing branch, and if 0-day is > happy with this, will move it to my "real" driver-core-next branch in a > day or so to get included in linux-next. I have been slow in getting my review out. This patch series is not yet ready for sending to Linus, so if putting this in linux-next implies that it will be in your next pull request to Linus, please do not put it in linux-next. Thanks, Frank > > thanks for sticking with this! > > greg k-h >
