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

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Date:	Fri, 6 Jul 2012 09:17:18 -0700
From:	Greg KH <greg@...ah.com>
To:	Jia Hongtao-B38951 <B38951@...escale.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

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?

greg k-h
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