linux-kernel - Re: [PATCH V3 5/6] Avoid duplicate probe for of platform devices

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Date:	Mon, 09 Jul 2012 08:58:11 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Li Yang-R58472 <r58472@...escale.com>
CC:	Jia Hongtao-B38951 <B38951@...escale.com>,
	Greg KH <greg@...ah.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.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:
>>> 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?

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

Rob
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