Re: [PATCH v3 2/2] PCI: of: Attach created of_node to existing device

[Greg Kroah-Hartman]

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@d0070000
> > > + pci0000:00
> > >   + 0000:00:00.0
> > >     + of_node -> .../devicetree/base/soc/pcie@d0070000/pci@0,0
> > >     + 0000:01:00.0
> > >       + of_node -> .../devicetree/base/soc/pcie@d0070000/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@xxxxxxxxxxxxxxx
> > > Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>
> > 
> > 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?

thanks,

greg k-h