On Sat, Jan 17, 2015 at 09:44:00AM +0100, Hans de Goede wrote: > Dear udev developers, > > We (me and some kernel devs mostly) would like to add support to > the kernel for userspace telling the kernel that it is done with > the *initial* loading of modules, with the purpose of cleaning up > (disabling) unused harware resources like e.g. regulators and > clocks. But you don't "know" when that happens. Especially with discoverable busses (PCI, USB, etc.), you know this :) > Currently the kernel does this cleanup just before it starts init > (which may very well be init from a ramdisk). In some cases this > is too early really, because later on a module may get loaded > which needs this resources, these resources will then get turned > on again by the loaded driver, and most of the time this is not > an issue, but sometimes it is. > > I realize very well that there is no magic moment where udev is > really ever done loading modules, but the case which we want to > support only involves devices which are *already enumerated*, but > may not yet have a driver loaded, when udev starts. We would like > udev to emit a signal (ABI to be discussed) when it is done > trying to load modules for everything which was already enumerated > when it starts, iow when there are no new device events pending > anymore when udev does its initial hotplug replay. The kernel doesn't even "know" when this type of thing is, how can udev know this? > So the question to you is would you be willing to include such > functionality in udev ? Note this signal would need to be emitted > when udev from the real rootfs is done with the initial module > loading, as the real rootfs may very well have more modules > available then the initrd. > > ### > > With the generic story above told let me also give the concrete > example / problem which has let to me asking this (note this has > been brought up before on various kernel lists, it is a > re-occuring theme, this is just an example really) : > > The problem at hand is a sata connector which also has a sata-power > connector on an embedded (ish) board where the sata-power is > controlled through a gpio. The sata-power connector is modeled > in devicetree as a power-supply and this supply gets controlled > by the ahci_platform driver. > > The disk power may very well have already been turned on by the > bootloader, so we add a regulator-boot-on property to the regulator > node in devicetree to make sure that it is left untouched when the > regulator driver loads. If the ahci_platform driver is build into > the kernel, it will then take control of the regulator and > everything works well. > > If however the ahci_platform driver is a module, then as soon as > the kernel is ready to start init, unused regulators are turned off > and the disk looses its power while spinning and ends up doing an > emergency heads park. What turns off the power in this situation? The kernel? Or userspace? Don't you have control of this? Have you tried to even create a patch that could do this type of thing to udev to see if it is even possible? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
