On 6 August 2015 at 22:14, Rob Herring <robherring2@xxxxxxxxx> wrote: > On Thu, Aug 6, 2015 at 9:11 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 >> fwnode_ensure_device() 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 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 these patches to kernelci.org and I'm >> currently trying to fix all regressions, usually due to code assuming >> that devices will be probed in a specific order. Current results [6] are >> 348 passes, 30 fails and 42 unknowns (linux-next [7] is currently >> 387/3/23). > > This is a bit worrying. If this causes a high number of boot failures, > fixing the errors you can find is not the path forward as we can't > test a lot of platforms (and many people don't look at -next). We may > want to put this behind a kconfig option so that we can easily restore > old behavior it needed. Otherwise, we could have to revert the series. A Kconfig sounds fine to me. Altogether, I don't think it's that bad because only these boards are known to have broken because of this series: at91-sama5d3_xplained sama5d35ek ste-snowball vexpress-v2p-ca15 vexpress-v2p-ca15 vexpress-v2p-ca15_a7 vexpress-v2p-ca15-tc1 vexpress-v2p-ca9 I assume there's only 3 different bugs to fix there, plus a race in imx boards that I have only papered over with a delay so far. The failure rate seems to be so high because each boot is a combination of board+defconfig and there are duplicated boards in several labs and many were just offline at that moment. But I agree that there's no way I can test it on all supported hw, so a Kconfig that people can quickly switch on to disable the feature sounds good to me. > Are all the commits before this series fixing boot failures? You can't > do dts updates as the fix or backwards compatibility will be broken. The gpio-ranges fix for Tegra has a commit that safeguards backwards compatibility, and the typo in regulator names for ux500 doesn't really break anything that I can see, I just stumped into it when trying to blindly fix the boot for ste-snowball (I don't have access to that hw). >> 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-v5 >> >> [6] http://kernelci.org/boot/all/job/collabora/kernel/v4.2-rc5-6548-g632b98c83840/ >> >> [7] http://kernelci.org/boot/all/job/next/kernel/next-20150806/ >> >> Changes in v3: >> - Only delay platform devices with OF nodes >> - Set and use device_node.platform_dev instead of reversing the logic to >> find the platform device that encloses a device node. > > I still want this to be a struct device and not a struct > platform_device and am not convinced it can't be. It can simply be an > optimization of the existing function: Now I realize what you meant, that makes sense to me. Thanks, Tomeu > struct platform_device *of_find_device_by_node(struct device_node *np) > { > if (node->device && node->device->bus == &platform_bus_type) > return to_platform_device(node->device); > return NULL; > } > > 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
