On Tue, Oct 13, 2015 at 2:57 PM, Tomeu Vizoso
[off-list ref] wrote:

On 26 September 2015 at 20:17, Rob Herring [off-list ref] wrote:

quoted

On 09/21/2015 09:02 AM, Tomeu Vizoso wrote:

quoted

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.

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.

Agreed.

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

Mainly Greg.

Please send me a pull req. I want to get this into -next and can
always drop it if there is further review.

Rob