[PATCH v6 0/22] On-demand device probing

[Tomeu Vizoso]

On 26 September 2015 at 21:22, Greg Kroah-Hartman
<gregkh at linuxfoundation.org> wrote:
> On Sat, Sep 26, 2015 at 01:17:04PM -0500, Rob Herring 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 (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 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.
>>
>> 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.
>
> Let me review this on Monday and I'll let you know...

Hi Greg, hope you don't mind that I ping you regarding this, just in
case it fell through some crack.

Regards,

Tomeu

> thanks,
>
> greg k-h
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