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][6][7] with these patches on top of friday's linux-next (20150925) to kernelci.org and I don't see any issues that could be caused by them. 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-v9 [6] http://kernelci.org/boot/all/job/collabora/kernel/v4.3-rc2-3497-g96d8df1bbcc1/ [7] http://kernelci.org/boot/all/job/next/kernel/next-20150925 Changes in v7: - Move IS_ENABLED(CONFIG_DELAY_DEVICE_PROBES) into if condition - Hide CONFIG_DELAY_DEVICE_PROBES behind EXPERT - Removed patch that moved deferred probe processing to device_initcall_sync, as it's not currently needed and can be applied later if we find any boards that fail to boot without this change. Changes in v6: - Drop bus_type.pre_probe and read the periphid in match() instead as suggested by Alan Stern. Changes in v5: - Set the pointer to struct device also for AMBA devices - Unset the pointer to struct device when the platform device is about to be unregistered - Increase the reference count of the device before returning from of_find_device_by_node() - Move the assignment to device_node->device for AMBA devices to another commit. - Hold a reference to the struct device while it's in use in of_device_probe(). 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. - Rename of_platform_probe to of_device_probe - Use device_node.device instead of device_node.platform_dev - Add Kconfig DELAY_DEVICE_PROBES to allow disabling delayed probing in machines with initcalls that depend on devices probing at a given time. - Also defer probes of AMBA devices registered from the DT as they can also request resources. Changes in v3: - Set and use device_node.platform_dev instead of reversing the logic to find the platform device that encloses a device node. - Drop the fwnode API to probe firmware nodes and add OF-only API for now. I think this same scheme could be used for machines with ACPI, but I haven't been able to find one that had to defer its probes because of the device probe order. Tomeu Vizoso (20): driver core: handle -EPROBE_DEFER from bus_type.match() ARM: amba: Move reading of periphid to amba_match() of/platform: Point to struct device from device node of: add function to allow probing a device from a OF node gpio: Probe GPIO drivers on demand pinctrl: Probe pinctrl devices on demand regulator: core: Probe regulators on demand drm: Probe panels on demand drm/tegra: Probe dpaux devices on demand i2c: core: Probe i2c adapters and devices on demand pwm: Probe PWM chip devices on demand backlight: Probe backlight devices on demand usb: phy: Probe phy devices on demand clk: Probe clk providers on demand pinctrl: Probe pinctrl devices on demand phy: core: Probe phy providers on demand dma: of: Probe DMA controllers on demand power-supply: Probe power supplies on demand driver core: Allow deferring probes until late init of/platform: Defer probes of registered devices drivers/amba/bus.c | 88 +++++++++++++++++++------------------ drivers/base/Kconfig | 18 ++++++++ drivers/base/dd.c | 30 ++++++++++++- drivers/clk/clk.c | 3 ++ drivers/dma/of-dma.c | 3 ++ drivers/gpio/gpiolib-of.c | 5 +++ drivers/gpu/drm/drm_panel.c | 3 ++ drivers/gpu/drm/tegra/dpaux.c | 3 ++ drivers/i2c/i2c-core.c | 4 ++ drivers/of/device.c | 61 +++++++++++++++++++++++++ drivers/of/platform.c | 30 ++++++++----- drivers/phy/phy-core.c | 3 ++ drivers/pinctrl/devicetree.c | 3 ++ drivers/power/power_supply_core.c | 3 ++ drivers/pwm/core.c | 3 ++ drivers/regulator/core.c | 2 + drivers/usb/phy/phy.c | 3 ++ drivers/video/backlight/backlight.c | 3 ++ include/linux/device.h | 4 +- include/linux/of.h | 1 + include/linux/of_device.h | 3 ++ 21 files changed, 219 insertions(+), 57 deletions(-) -- 2.4.3 -- 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
