On 9 September 2015 at 03:33, Rob Herring [off-list ref] wrote:

On 09/08/2015 02:30 AM, Tomeu Vizoso wrote:

quoted

On 7 September 2015 at 22:50, Rob Herring [off-list ref] wrote:

quoted

On Mon, Sep 7, 2015 at 7:23 AM, Tomeu Vizoso [off-list ref] 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] with only these patches on top of thursday's
linux-next to kernelci.org and I don't see any issues that could be
caused by them. For some reason it currently has more passes than the
version of -next it's based on!

With this series I get the kernel to output to the panel in 0.5s,
instead of 2.8s.

Regards,

Tomeu

[0] http://lists.freedesktop.org/archives/dri-devel/2014-August/066527.html

[1] https://lkml.org/lkml/2014/5/12/452

[2] https://lkml.org/lkml/2015/6/17/305

[3] http://article.gmane.org/gmane.linux.ports.arm.kernel/277689

[4] https://lkml.org/lkml/2015/7/21/441a

[5] https://git.collabora.com/cgit/user/tomeu/linux.git/log/?h=on-demand-probes-v6

[6] http://kernelci.org/boot/all/job/collabora/kernel/v4.2-11902-g25d80c927f8b/

[7] http://kernelci.org/boot/all/job/next/kernel/next-20150903/

Changes in v4:
- Added bus.pre_probe callback so the probes of Primecell devices can be
  deferred if their device IDs cannot be yet read because of the clock
  driver not having probed when they are registered. Maybe this goes
  overboard and the matching information should be in the DT if there is
  one.

Seems overboard to me or at least a separate problem.

It's a separate problem but this was preventing the series from
working on a few boards.

What is the failure? Not booting? Fixing not working would certainly not
be overboard.

On the device I was testing on (qemu's vexpress-a15 machine) the
machine booted and I was able to open a ssh session, but serial was
broken among other AMBA devices:

/memory-controller at 2b0a0000
/memory-controller at 7ffd0000
/dma at 7ffb0000
/smb/motherboard/iofpga at 3,00000000/sysctl at 020000
/smb/motherboard/iofpga at 3,00000000/aaci at 040000
/smb/motherboard/iofpga at 3,00000000/mmci at 050000
/smb/motherboard/iofpga at 3,00000000/kmi at 060000
/smb/motherboard/iofpga at 3,00000000/kmi at 070000
/smb/motherboard/iofpga at 3,00000000/uart at 090000
/smb/motherboard/iofpga at 3,00000000/uart at 0a0000
/smb/motherboard/iofpga at 3,00000000/uart at 0b0000
/smb/motherboard/iofpga at 3,00000000/uart at 0c0000
/smb/motherboard/iofpga at 3,00000000/wdt at 0f0000
/smb/motherboard/iofpga at 3,00000000/timer at 110000
/smb/motherboard/iofpga at 3,00000000/timer at 120000
/smb/motherboard/iofpga at 3,00000000/rtc at 170000
/smb/motherboard/iofpga at 3,00000000/clcd at 1f0000

Another way of avoiding this particular problem would be not delaying
the probe of devices in the configuration bus, by doing something like
this:

diff --git a/drivers/bus/vexpress-config.c b/drivers/bus/vexpress-config.c
index 6575c0fe6a4e..eda293869cd3 100644
--- a/drivers/bus/vexpress-config.c
+++ b/drivers/bus/vexpress-config.c

@@ -181,7 +181,7 @@ static int vexpress_config_populate(struct

device_node *node)
        if (WARN_ON(!parent))
                return -ENODEV;

-       return of_platform_populate(node, NULL, NULL, parent);
+       return of_platform_populate_early(node, NULL, NULL, parent);
 }

 static int __init vexpress_config_init(void)

But I think this would be papering over the underlying issue and it
would be better to have proper explicit dependencies.

Regards,

Tomeu

quoted

quoted

Most clocks have
to be setup before the driver model simply because timers depend on
clocks usually.

Yes, but in this case the apb clocks for the primecell devices are
implemented in a normal platform driver (vexpress_osc_driver), instead
of using CLK_OF_DECLARE.

Okay.

Rob

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