Re: [PATCH v2] usb: core: add USB_QUIRK_NO_BOS for devices that hang on BOS descriptor

[Michal Pecio <michal.pecio@gmail.com>]

On Mon, 8 Dec 2025 06:12:15 +0900, Greg KH wrote:
> Ok, I can duplicate this here.  Maybe we just don't ask for the BOS
> descriptor if no one needs/asks for it.  I can play with that later
> and see if that helps as I'm sure this isn't going to be the only
> device that can't handle the BOS descriptor if Windows isn't querying
> for it, so we don't want to make a huge quirk table if we don't have
> to.

Hi Greg and others,

The workaround is now in, but if somebody is interested in getting rid
of it, it might suffice to make kernel BOS requests more Windows-like,
since these devices work fine with Windows (and Windows queries BOS).

By monitoring Windows 10 in a VM I found two key differences: Windows
fetches BOS *after* the configuration descriptor, and it requests 255
bytes at once in its first attempt (there is likely a second attempt
if BOS length exceeds 255, but I don't have such a device to test).

Any chance that the change below is enough for these video grabbers?

THB I suspect that it's the ordering which matters (the devices respond
to BOS queries by lsusb after enumeration), but implementing that seems
a little more complicated, so let's try the size first.

Regards,
Michal


diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 45e20c6d76c0..ca42e89399d0 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -1037,16 +1037,15 @@ int usb_get_bos_descriptor(struct usb_device *dev)
 	int ret;
 
 	if (dev->quirks & USB_QUIRK_NO_BOS) {
-		dev_dbg(ddev, "skipping BOS descriptor\n");
-		return -ENOMSG;
+		dev_info(ddev, "NOT skipping BOS descriptor\n");
 	}
 
-	bos = kzalloc_obj(*bos);
+	bos = kzalloc(255, GFP_KERNEL);
 	if (!bos)
 		return -ENOMEM;
 
 	/* Get BOS descriptor */
-	ret = usb_get_descriptor(dev, USB_DT_BOS, 0, bos, USB_DT_BOS_SIZE);
+	ret = usb_get_descriptor(dev, USB_DT_BOS, 0, bos, 255);
 	if (ret < USB_DT_BOS_SIZE || bos->bLength < USB_DT_BOS_SIZE) {
 		dev_notice(ddev, "unable to get BOS descriptor or descriptor too short\n");
 		if (ret >= 0)