On 26 September 2015 at 21:22, Greg Kroah-Hartman
[off-list ref] wrote:

On Sat, Sep 26, 2015 at 01:17:04PM -0500, Rob Herring 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 (St?phane 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo at vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/