[PATCH] usb: core: Notify through uevent when not enough bandwidth available

[PATCH] usb: core: Notify through uevent when not enough bandwidth available

[Nícolas F. R. A. Prado]

Currently, when a new device is plugged in and the host controller can't
find enough bandwidth for it, an error message is printed:

  usb 1-3: Not enough bandwidth for new device state.

In order to allow userspace to react to this and suggest the user to use
a different host controller, send a uevent with
'USB_NOT_ENOUGH_BANDWIDTH=1' to the root hub device.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
---
 drivers/usb/core/hcd.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 8e8a5f59b319..a71605398540 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1825,6 +1825,13 @@ void usb_hcd_flush_endpoint(struct usb_device *udev,
 	}
 }
 
+static void not_enough_bandwidth_notify(struct usb_hcd *hcd)
+{
+	static char *envp[2] = { "USB_NOT_ENOUGH_BANDWIDTH=1", NULL };
+
+	kobject_uevent_env(&hcd->self.root_hub->dev.kobj, KOBJ_CHANGE, envp);
+}
+
 /**
  * usb_hcd_alloc_bandwidth - check whether a new bandwidth setting exceeds
  *				the bus bandwidth
@@ -1954,6 +1961,8 @@ int usb_hcd_alloc_bandwidth(struct usb_device *udev,
 		}
 	}
 	ret = hcd->driver->check_bandwidth(hcd, udev);
+	if (ret == -ENOSPC)
+		not_enough_bandwidth_notify(hcd);
 reset:
 	if (ret < 0)
 		hcd->driver->reset_bandwidth(hcd, udev);

---
base-commit: c425609d6ac4012c8bbf01ec2e10e801b1923a7b
change-id: 20260615-usb-notify-not-enough-bandwidth-5f39ccf6754b

Best regards,
-- 
Nícolas F. R. A. Prado <nfraprado@collabora.com>

Re: [PATCH] usb: core: Notify through uevent when not enough bandwidth available

[Greg Kroah-Hartman]

On Mon, Jun 15, 2026 at 10:35:33AM -0400, Nícolas F. R. A. Prado wrote:
> Currently, when a new device is plugged in and the host controller can't
> find enough bandwidth for it, an error message is printed:
> 
>   usb 1-3: Not enough bandwidth for new device state.
> 
> In order to allow userspace to react to this and suggest the user to use
> a different host controller, send a uevent with
> 'USB_NOT_ENOUGH_BANDWIDTH=1' to the root hub device.

Where is this new user/kernel api now documented?  And what tool is
going to be looking for it?

thanks,

greg k-h

Re: [PATCH] usb: core: Notify through uevent when not enough bandwidth available

[Nícolas F. R. A. Prado]

On Fri, 2026-07-10 at 15:01 +0200, Greg Kroah-Hartman wrote:
> On Mon, Jun 15, 2026 at 10:35:33AM -0400, Nícolas F. R. A. Prado
> wrote:
> > Currently, when a new device is plugged in and the host controller
> > can't
> > find enough bandwidth for it, an error message is printed:
> > 
> >   usb 1-3: Not enough bandwidth for new device state.
> > 
> > In order to allow userspace to react to this and suggest the user
> > to use
> > a different host controller, send a uevent with
> > 'USB_NOT_ENOUGH_BANDWIDTH=1' to the root hub device.
> 
> Where is this new user/kernel api now documented?  And what tool is
> going to be looking for it?

Sorry I missed that, I'll add the documentation at
Documentation/ABI/testing/usb-uevent in v2.

As for the user, Steam will use it.

-- 
Thanks,

Nícolas