[PATCH v2 0/22] On-demand device probing

[Rafael J. Wysocki]

On Tuesday, July 28, 2015 03:19:31 PM 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
> 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).
> 
> With this series I get the kernel to output to the panel in 0.5s,
> instead of 2.8s.

Can you trim your CC list somewhat, please?

I'm definitely going to look at this, but not before then next week.
Sorry about that.

Thanks,
Rafael