linux-kernel - Re: [PATCH v3 2/2] PCI: of: Attach created of

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Date: Fri, 12 Apr 2024 10:10:19 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Rob Herring <robh@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Lizhi Hou <lizhi.hou@....com>, Max
 Zhen <max.zhen@....com>, Sonal Santan <sonal.santan@....com>, Stefano
 Stabellini <stefano.stabellini@...inx.com>, Jonathan Cameron
 <Jonathan.Cameron@...wei.com>, Krzysztof Wilczyński
 <kwilczynski@...nel.org>, linux-kernel@...r.kernel.org,
 linux-pci@...r.kernel.org, Allan Nielsen <allan.nielsen@...rochip.com>,
 Horatiu Vultur <horatiu.vultur@...rochip.com>, Steen Hegelund
 <steen.hegelund@...rochip.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, stable@...r.kernel.org
Subject: Re: [PATCH v3 2/2] PCI: of: Attach created of_node to existing
 device

Hi Greg, Rob,

On Fri, 12 Apr 2024 09:41:19 +0200
Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:

> On Thu, Apr 11, 2024 at 03:34:49PM -0500, Rob Herring wrote:
> > On Thu, Apr 11, 2024 at 03:23:55PM +0200, Greg Kroah-Hartman wrote:  
> > > On Mon, Mar 25, 2024 at 04:39:15PM +0100, Herve Codina wrote:  
> > > > The commit 407d1a51921e ("PCI: Create device tree node for bridge")
> > > > creates of_node for PCI devices.
> > > > 
> > > > During the insertion handling of these new DT nodes done by of_platform,
> > > > new devices (struct device) are created. For each PCI devices a struct
> > > > device is already present (created and handled by the PCI core).
> > > > Having a second struct device to represent the exact same PCI device is
> > > > not correct.
> > > > 
> > > > On the of_node creation:
> > > > - tell the of_platform that there is no need to create a device for this
> > > >   node (OF_POPULATED flag),
> > > > - link this newly created of_node to the already present device,
> > > > - tell fwnode that the device attached to this of_node is ready using
> > > >   fwnode_dev_initialized().
> > > > 
> > > > With this fix, the of_node are available in the sysfs device tree:
> > > > /sys/devices/platform/soc/d0070000.pcie/
> > > > + of_node -> .../devicetree/base/soc/pcie@...70000
> > > > + pci0000:00
> > > >   + 0000:00:00.0
> > > >     + of_node -> .../devicetree/base/soc/pcie@...70000/pci@0,0
> > > >     + 0000:01:00.0
> > > >       + of_node -> .../devicetree/base/soc/pcie@...70000/pci@0,0/dev@0,0
> > > > 
> > > > On the of_node removal, revert the operations.
> > > > 
> > > > Fixes: 407d1a51921e ("PCI: Create device tree node for bridge")
> > > > Cc: stable@...r.kernel.org
> > > > Signed-off-by: Herve Codina <herve.codina@...tlin.com>  
> > > 
> > > I need an ack from the maintainer here before I can take this.  
> > 
> > Correct me if I'm wrong, but having the of_node sysfs link populated or 
> > changed after device_add is a race we lost. Userspace is notified about 
> > the new device and then some time later the symlink shows up.  
> 
> Ah, yes, I missed that, good catch, this will not work.
> 
> > However, it so far is not appearing that there's an easy way to 
> > reshuffle order of things to fix this.
> > 
> > Maybe the short term (and stable) answer just don't create any of_node 
> > symlinks on these dynamically created nodes.  
> 
> That would work, but does userspace really need to know this
> information?
> 

I don't think that the user space really need this information.
I agree, it should work.

Let me rework my series in that sense and perform some tests before
sending a new iteration removing the of_node sysfs link creation.

Best regards,
Hervé