On 7 September 2015 at 22:50, Rob Herring <robherring2@xxxxxxxxx> wrote: > 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. It's a separate problem but this was preventing the series from working on a few boards. > Most clocks have > to be setup before the driver model simply because timers depend on > clocks usually. Yes, but in this case the apb clocks for the primecell devices are implemented in a normal platform driver (vexpress_osc_driver), instead of using CLK_OF_DECLARE. Regards, Tomeu > Rob > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- 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
