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

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Date:	Mon, 9 Jul 2012 02:34:39 +0000
From:	Jia Hongtao-B38951 <B38951@...escale.com>
To:	Greg KH <greg@...ah.com>
CC:	Rob Herring <robherring2@...il.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Li Yang-R58472 <r58472@...escale.com>
Subject: RE: [PATCH V3 5/6] Avoid duplicate probe for of platform devices


> -----Original Message-----
> From: Greg KH [mailto:greg@...ah.com]
> Sent: Saturday, July 07, 2012 12:17 AM
> To: Jia Hongtao-B38951
> Cc: Rob Herring; devicetree-discuss@...ts.ozlabs.org; linux-
> kernel@...r.kernel.org; Li Yang-R58472
> Subject: Re: [PATCH V3 5/6] Avoid duplicate probe for of platform devices
> 
> On Fri, Jul 06, 2012 at 06:07:43AM +0000, Jia Hongtao-B38951 wrote:
> >
> > > -----Original Message-----
> > > From: Greg KH [mailto:greg@...ah.com]
> > > Sent: Friday, July 06, 2012 12:26 PM
> > > To: Jia Hongtao-B38951
> > > Cc: Rob Herring; devicetree-discuss@...ts.ozlabs.org; linux-
> > > kernel@...r.kernel.org; Li Yang-R58472
> > > Subject: Re: [PATCH V3 5/6] Avoid duplicate probe for of platform
> devices
> > >
> > > On Fri, Jul 06, 2012 at 02:05:05AM +0000, Jia Hongtao-B38951 wrote:
> > > > Hi Rob and Greg KH,
> > > >
> > > > Do you have any better idea to avoid duplication probe warning?
> > >
> > > I have no idea what the problem is that you are trying to solve.
> > >
> > > > > On 06/08/2012 04:43 AM, Jia Hongtao wrote:
> > > > > > We changed the pcie controller driver to platform driver so
> that
> > > the
> > > > > PCI
> > > > > > of platform devices need to be created earlier in the
> arch_initcall
> > > > > stage
> > > > > > according to the original timing of calling fsl_add_bridge().
> So we
> > > do
> > > > > PCI
> > > > > > probing separately from other devices. But probing more than
> once
> > > could
> > > > > > cause duplication warning. We add check if the devices have
> already
> > > > > probed
> > > > > > before probing any devices to avoid duplication warning.
> > >
> > > Ick, something else is going wrong here, how could you ever have the
> > > same device probed more than once?
> > >
> > > > > > Signed-off-by: Jia Hongtao <B38951@...escale.com>
> > > > > > Signed-off-by: Li Yang <leoli@...escale.com>
> > > > > > ---
> > > > >
> > > > > Where's v1 and v2 history?
> > > > >
> > > > > >  drivers/of/platform.c |   18 ++++++++++++------
> > > > > >  1 files changed, 12 insertions(+), 6 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > > > > > index a37330e..3aab01f 100644
> > > > > > --- a/drivers/of/platform.c
> > > > > > +++ b/drivers/of/platform.c
> > > > > > @@ -139,6 +139,18 @@ struct platform_device
> *of_device_alloc(struct
> > > > > device_node *np,
> > > > > >  	if (!dev)
> > > > > >  		return NULL;
> > > > > >
> > > > > > +	dev->dev.of_node = of_node_get(np);
> > > > > > +	if (bus_id)
> > > > > > +		dev_set_name(&dev->dev, "%s", bus_id);
> > > > > > +	else
> > > > > > +		of_device_make_bus_id(&dev->dev);
> > > > > > +
> > > > > > +	if (kset_find_obj(dev->dev.kobj.kset, kobject_name(&dev-
> > > >dev.kobj)))
> > >
> > > Whatever you are trying to do here, odds are, it's wrong :)
> > >
> > > What is happening that is causing the problem?  What is causing the
> > > platform core to be calling probe on a device more than once?
> > >
> > > greg k-h
> >
> > This is why in some cases we may probe twice:
> > Firstly, we need to probe pci controller separately. But in KVM
> different
> > topology of device tree is used in which pci nodes are not under root
> node
> > but under "simple bus". Unfortunately, of_platform_bus_probe() will
> probe
> > all the first level nodes under "simple bus" so pci nodes will probe
> again.
> 
> Sounds like a bug :)
> 
> > Two ways to solve this problem:
> > 1. All the nodes that need to be probed should just under root.
> 
> That seems reasonable.
> 
> > 2. Avoid duplication probe at runtime like this patch did.
> 
> No, don't paper over the real problem in the platform core code like
> this.  Fix the real issue here instead.
> 
> > I do like the first one but it's hard to changing the traditional way
> that
> > exist for a long time.
> 
> 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/

- Jia Hongtao.

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