On Mon, Sep 7, 2015 at 7:23 AM, Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx> wrote: > Hello, > > I have a problem with the panel on my Tegra Chromebook taking longer > than expected to be ready during boot (Stéphane Marchesin reported what > is basically the same issue in [0]), and have looked into ordered > probing as a better way of solving this than moving nodes around in the > DT or playing with initcall levels and linking order. > > While reading the thread [1] that Alexander Holler started with his > series to make probing order deterministic, it occurred to me that it > should be possible to achieve the same by probing devices as they are > referenced by other devices. > > This basically reuses the information that is already implicit in the > probe() implementations, saving us from refactoring existing drivers or > adding information to DTBs. > > During review of v1 of this series Linus Walleij suggested that it > should be the device driver core to make sure that dependencies are > ready before probing a device. I gave this idea a try [2] but Mark Brown > pointed out to the logic duplication between the resource acquisition > and dependency discovery code paths (though I think it's fairly minor). > > To address that code duplication I experimented with Arnd's devm_probe > [3] concept of having drivers declare their dependencies instead of > acquiring them during probe, and while it worked [4], I don't think we > end up winning anything when compared to just probing devices on-demand > from resource getters. > > One remaining objection is to the "sprinkling" of calls to > of_device_probe() in the resource getters of each subsystem, but I think > it's the right thing to do given that the storage of resources is > currently subsystem-specific. > > We could avoid the above by moving resource storage into the core, but I > don't think there's a compelling case for that. > > I have tested this on boards with Tegra, iMX.6, Exynos, Rockchip and > OMAP SoCs, and these patches were enough to eliminate all the deferred > probes (except one in PandaBoard because omap_dma_system doesn't have a > firmware node as of yet). > > Have submitted a branch [5] with only these patches on top of thursday's > linux-next to kernelci.org and I don't see any issues that could be > caused by them. For some reason it currently has more passes than the > version of -next it's based on! > > With this series I get the kernel to output to the panel in 0.5s, > instead of 2.8s. > > Regards, > > Tomeu > > [0] http://lists.freedesktop.org/archives/dri-devel/2014-August/066527.html > > [1] https://lkml.org/lkml/2014/5/12/452 > > [2] https://lkml.org/lkml/2015/6/17/305 > > [3] http://article.gmane.org/gmane.linux.ports.arm.kernel/277689 > > [4] https://lkml.org/lkml/2015/7/21/441a > > [5] https://git.collabora.com/cgit/user/tomeu/linux.git/log/?h=on-demand-probes-v6 > > [6] http://kernelci.org/boot/all/job/collabora/kernel/v4.2-11902-g25d80c927f8b/ > > [7] http://kernelci.org/boot/all/job/next/kernel/next-20150903/ > > Changes in v4: > - Added bus.pre_probe callback so the probes of Primecell devices can be > deferred if their device IDs cannot be yet read because of the clock > driver not having probed when they are registered. Maybe this goes > overboard and the matching information should be in the DT if there is > one. Seems overboard to me or at least a separate problem. Most clocks have to be setup before the driver model simply because timers depend on clocks usually. Rob -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
