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

    thanks,

    greg k-h


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