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Date:	Tue, 13 Oct 2015 21:57:09 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Rob Herring <robh@...nel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Mark Brown <broonie@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-acpi@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v6 0/22] On-demand device probing

On 26 September 2015 at 20:17, Rob Herring <robh@...nel.org> wrote:
> On 09/21/2015 09:02 AM, Tomeu Vizoso wrote:
>> Hello,
>>
>> I have a problem with the panel on my Tegra Chromebook taking longer
>> than expected to be ready during boot (St├ęphane 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 today's
>> linux-next (20150921) 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.
>
> I think we're pretty close other than some minor comments. I would like
> to see ack's from Greg and some reviewed-bys from others. The subsystem
> changes are minor and there has been plenty of chance to comment, so I
> don't think acks from all subsystems are needed.

Hi Rob,

I'm not sure we are going to get much more feedback by just waiting or
resending what has been sent so many times.

Did you have in mind specific people you wanted to see reviewed-bys from?

Guess Greg will get to this sometime soon.

Regards,

Tomeu

> Your branch is based on -next. Is there any dependence on something in
> -next? I want to get this into -next soon, but need a branch not based
> on -next. Please send me a pull request with the collected acks and
> minor comments I have addressed.
>
> Rob
>
>>
>> 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-v8
>>
>> [6] http://kernelci.org/boot/all/job/collabora/kernel/v4.3-rc2-2587-gf92b0ab33d14/
>>
>> [7] http://kernelci.org/boot/all/job/next/kernel/next-20150921
>>
>> Changes in v6:
>> - Drop bus_type.pre_probe and read the periphid in match() instead as
>>   suggested by Alan Stern.
>> - Merge changes to the regulator subsystem's locking so no references
>>   are leaked between commits.
>>
>> 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().
>> - Use regulator_class' klist of devices instead of regulator_list to
>>   store and lookup regulator devices.
>>
>> 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.
>> - Start processing deferred probes in device_initcall_sync
>> - 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 (22):
>>   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
>>   gpio: Probe pinctrl devices on demand
>>   regulator: core: Remove regulator_list
>>   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
>>   driver core: Start processing deferred probes earlier
>>   of/platform: Defer probes of registered devices
>>
>>  drivers/amba/bus.c                  |  88 ++++++------
>>  drivers/base/Kconfig                |  18 +++
>>  drivers/base/dd.c                   |  35 ++++-
>>  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            | 257 +++++++++++++++++++++++-------------
>>  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, 386 insertions(+), 150 deletions(-)
>>
>
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