RE: [PATCH V3 5/6] Avoid duplicate probe for of platform devices

-----Original Message-----
From: Rob Herring [mailto:robherring2@gmail.com]
Sent: Monday, July 09, 2012 9:58 PM
To: Li Yang-R58472
Cc: Jia Hongtao-B38951; Greg KH; devicetree-discuss@lists.ozlabs.org;
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V3 5/6] Avoid duplicate probe for of platform devices

On 07/08/2012 10:46 PM, Li Yang-R58472 wrote:

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I don't understand, why is this just showing up now?  What
changed to cause this?  Couldn't that be the real problem here?

The issue is showing up because we now probe devices twice.
Previously, we just probe devices once. But now we changed the way
of pci init which makes pci controllers should be probed earlier
than other devices. So we have to probe pci nodes separately. Probe
more than once is the root cause of this issue.

The pci patchset I mentioned please refer to:
http://patchwork.ozlabs.org/patch/163742/

Let me try to clarify a little bit.  The of platform bus normally
traverse the device tree to add all the devices.  The change which
caused problem is that we need to probe PCIe RC devices at a earlier
stage of initialization.  So we added these PCIe RC devices earlier
than the normal device tree traversal process.  These PCIe RC devices
will be scanned again during the normal traversal and cause
duplicated devices being added.  Our proposal is to deal with
duplicated devices automatically and make it possible to scan the
device tree multiple times for devices to be added.

What is making PCI need to be probed earlier? Perhaps deferred probe
would work?

Pci initialization fsl_add_bridge() should be called earlier as they used
to be called in board specific code xx_setup_arch(). Now we put this init
part in the probe function of pci controller to make the code infrastructure
better. That make pci bus should be probed earlier.

Perhaps giving of_platform_populate an exclude list of compatible
strings to skip would work.

Rob

Yes, this would work and we actually already implemented this solution.
But I think it looks hackish and will influence the other API users.

Thanks.
-Jia Hongtao.