linux-kernel - Re: [PATCH] USB: of: filter disabled device node

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Message-ID: <CAD48c-UgjXdPuKswm9_KgPT2xkWR4Aie1fG5p9AGRgukFs-gOw@mail.gmail.com>
Date: Sat, 22 Nov 2025 21:15:29 +0800
From: jerry xzq <jerry.xzq@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: of: filter disabled device node

On Sat, Nov 22, 2025 at 8:34 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Sat, Nov 22, 2025 at 07:31:47PM +0800, jerry xzq wrote:
> > On Sat, Nov 22, 2025 at 7:26 PM Zhengqiao Xia <jerry.xzq@...il.com> wrote:
> >
> > > We should not point the of_node of a USB device to a disabled devicetree
> > > node. Otherwise, the interface under this USB device will not be able
> > > to register.
> > >
> > > Signed-off-by: Zhengqiao Xia <jerry.xzq@...il.com>
> > > ---
> > >  drivers/usb/core/of.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/usb/core/of.c b/drivers/usb/core/of.c
> > > index 763e4122ed5b3..6bb577e711811 100644
> > > --- a/drivers/usb/core/of.c
> > > +++ b/drivers/usb/core/of.c
> > > @@ -31,6 +31,9 @@ struct device_node *usb_of_get_device_node(struct
> > > usb_device *hub, int port1)
> > >                 if (of_property_read_u32(node, "reg", &reg))
> > >                         continue;
> > >
> > > +               if (!of_device_is_available(node))
> > > +                       continue;
> > > +
> > >                 if (reg == port1)
> > >                         return node;
> > >         }
> > > --
> > > 2.34.1
> > >
> > >  Supplementing questions from the previous email:
> >
> > > What changed to require this?  What commit id does this fix?
> > > And what devices have a disabled devicetree node?
> >
> > fixes: 01fdf179f4b064d4c9d30(usb: core: skip interfaces disabled in
> > devicetree )
> >
> > Connect a USB device directly to the USB port, for me, LTE RW101.
>
> Why?  Why not just us the normal USB device topology?  Why is this in DT
> at all?
This is why I need to disable this USB hub node.  I didn't want this
node to work properly, so I disabled it.

>
> > However, a disabled node is attached to the DTS node of this port.
>
> Why?
please see:
https://github.com/torvalds/linux/blob/master/drivers/usb/core/usb.c#L731
https://github.com/torvalds/linux/blob/master/drivers/usb/core/of.c#L25

>
> > &xhci3 {
> >         status = "okay";
> >
> >         /* 2.x hub on port 1 */
> >         usb_hub_2_x: hub@1 {
> >                 compatible = "usbbda,5411";
> >                 reg = <1>;
> >                 vdd-supply = <&pp3300_s3>;
> >                 peer-hub = <&usb_hub_3_x>;
> >                 status = "disabled";
> >
> >                 ports {
> >                         #address-cells = <1>;
> >                         #size-cells = <0>;
> >                         port@1 {
> >                                 reg = <1>;
> >                                 usb_hub_dsp1_hs: endpoint { };
> >                         };
> >                         port@2 {
> >                                 reg = <2>;
> >                                 usb_hub_dsp2_hs: endpoint { };
> >                         };
> >                         port@3 {
> >                                 reg = <3>;
> >                                 usb_hub_dsp3_hs: endpoint { };
> >                         };
> >                         port@4 {
> >                                 reg = <4>;
> >
> >                                 /* On-board WWAN card */
> >                                 usb_hub_dsp4_hs: endpoint { };
>
> That's the thing I don't want to see, why is that WWAN card described
> here?  Why can't the normal USB device discovery find it and use it
> properly?

I want to disable the whole hub.

>
> >                         };
> >                 };
> >         };
> >
> > Based on the current code, the of_node of this directly connected LTE
> > device is hub.
>
> But why is that needed?
this is the behavior of code:
please see:
https://github.com/torvalds/linux/blob/master/drivers/usb/core/usb.c#L731
https://github.com/torvalds/linux/blob/master/drivers/usb/core/of.c#L25

>
> > If there is only one LTE interface, then the of_node of this interface
> > is also the hub.
>
> Again, why?
please see: https://github.com/torvalds/linux/blob/master/drivers/usb/core/of.c#L57
>
> > With the following code, the interface will be unable to create a device.
> >
> > if (intf->dev.of_node &&
> > !of_device_is_available(intf->dev.of_node)) {
> > dev_info(&dev->dev, "skipping disabled interface %d\n",
> > intf->cur_altsetting->desc.bInterfaceNumber);
> > continue;
> > }
> > Then this LTE will be unable to create a device.
> > this is not the result I wanted.
>
> Then try removing it from dt entirely, it should not be necessary to
> describe USB devices in dt.
>
> thanks,
>
> greg k-h