usb: misc: onboard_usb_hub: Don't defer probing for 'incomplete' DT nodes

Some boards have device tree nodes for USB hubs supported by the
onboard_usb_hub driver, but the nodes don't have all properties
needed for the driver to work properly (which is not necessarily
an error in the DT). Currently _find_onboard_hub() returns
-EPROBE_DEFER in such cases, which results in an unusable USB hub,
since successive probes fail in the same way. Use the absence of
the "vdd" supply as an indicator of such 'incomplete' DT nodes
and return -ENODEV.

Fixes: 8bc063641ceb ("usb: misc: Add onboard_usb_hub driver")
Reported-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---

 drivers/usb/misc/onboard_usb_hub.c | 9 +++++++++
 1 file changed, 9 insertions(+)

On Tue, Dec 20, 2022 at 02:15:19PM +0000, Matthias Kaehlcke wrote:
> Hi Johan,
> 
> On Tue, Dec 20, 2022 at 08:55:52AM +0100, Johan Hovold wrote:
> > On Tue, Dec 20, 2022 at 12:45:01AM +0000, Matthias Kaehlcke wrote:
> > > Some boards have device tree nodes for USB hubs supported by the
> > > onboard_usb_hub driver, but the nodes don't have all properties
> > > needed for the driver to work properly (which is not necessarily
> > > an error in the DT). Currently _find_onboard_hub() returns
> > > -EPROBE_DEFER in such cases, which results in an unusable USB hub,
> > > since successive probes fail in the same way. Use the absence of
> > > the "vdd" supply as an indicator of such 'incomplete' DT nodes
> > > and return -ENODEV.
> > > 
> > > Fixes: 8bc063641ceb ("usb: misc: Add onboard_usb_hub driver")
> > > Reported-by: Stefan Wahren <stefan.wahren@i2se.com>
> > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > > ---
> > > 
> > >  drivers/usb/misc/onboard_usb_hub.c | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> > > 
> > > diff --git a/drivers/usb/misc/onboard_usb_hub.c b/drivers/usb/misc/onboard_usb_hub.c
> > > index d63c63942af1..2968da515016 100644
> > > --- a/drivers/usb/misc/onboard_usb_hub.c
> > > +++ b/drivers/usb/misc/onboard_usb_hub.c
> > > @@ -363,6 +363,15 @@ static struct onboard_hub *_find_onboard_hub(struct device *dev)
> > >  	hub = dev_get_drvdata(&pdev->dev);
> > >  	put_device(&pdev->dev);
> > >  
> > > +	/*
> > > +	 * Some boards have device tree nodes for USB hubs supported by this
> > > +	 * driver, but the nodes don't have all properties needed for the driver
> > > +	 * to work properly. Use the absence of the "vdd" supply as an indicator
> > > +	 * of such nodes.
> > > +	 */
> > > +	if (!of_get_property(pdev->dev.of_node, "vdd", NULL))
> > > +		return ERR_PTR(-ENODEV);
> > 
> > Does this not break your original use case? Don't you want "vdd-supply"
> > here?
> 
> Ouch, yes it does (to a certain degree). Thanks for pointing it out. My
> sanity check didn't catch this because the platform driver still probes
> successfully and powers the hub on.
> 
> > That said, this seems like the wrong property to look for both in
> > principle and as it is described as optional by the binding:
> > 
> > 	Documentation/devicetree/bindings/usb/realtek,rts5411.yaml
> > 
> > It seems that you should use the compatible property and check that it
> > holds one of the expected values:
> > 
> >  - usbbda,5411
> >  - usbbda,411
> > 
> > rather than treat every hub node as describing a realtek hub (AFAIK,
> > there is no generic binding for this yet).
> 
> The driver only probes for specific hub models, among them the Microchip
> USB2514B hub with which Stefan encountered the regression [1].
> 
> My initial assumption when writing this driver was that the existence of
> a node for a supported hub means that the driver should be used. However
> the regression encountered by Stefan makes clear that this assumption is
> incorrect. It's not common, but a device tree may have nodes for onboard
> USB devices, among them hubs (which might become more common with this
> driver). Not in all instances the hub nodes were added with the intention
> of using this driver for power sequencing the hub (e.g. [2]). 

Yeah, you can't assume that. The DT bindings for USB has been around
since before your onboard-hub driver.

> The
> compatible string alone doesn't indicate that the onboard_hub driver
> should be instantiated for a given hub, which is why I'm using the
> existence of "vdd-supply" as indicator.

I don't have time to review this in details, but checking for a specific
supply like this just seems wrong (as other have since also pointed out
in comments to your v2). There could be hubs which just need to deassert
a reset pin for example, and some of the bindings do not even mandate a
regulator as I mentioned above.

Johan