Re: [PATCH] usb: core: Fix bandwidth for devices with invalid wBytesPerInterval

[Greg KH]

On Thu, Apr 02, 2026 at 10:14:00AM +0800, Tao Xue wrote:
> As specified in Section 4.14.2 of the xHCI Specification, the xHC
> reserves bandwidth for periodic endpoints according to bInterval and
> wBytesPerInterval (Max ESIT Payload).
> 
> Some peripherals report an invalid wBytesPerInterval in their device
> descriptor, which is either 0 or smaller than the actual data length
> transmitted. This issue is observed on ASIX AX88179 series USB 3.0
> Ethernet adapters.
> 
> These errors may lead to unexpected behavior on certain USB host
> controllers, causing USB peripherals to malfunction.
> 
> To address the issue, return max(wBytesPerInterval, max_payload) when
> calculating bandwidth reservation.
> 
> Fixes: 9238f25d5d32 ("USB: xhci: properly set endpoint context fields for periodic eps.")
> Cc: <stable@xxxxxxxxxx>
> Signed-off-by: Tao Xue <xuetao09@xxxxxxxxxx>
> ---
>  drivers/usb/core/usb.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
> index e9a10a33534c..8f2e05a5a015 100644
> --- a/drivers/usb/core/usb.c
> +++ b/drivers/usb/core/usb.c
> @@ -1125,6 +1125,8 @@ EXPORT_SYMBOL_GPL(usb_free_noncoherent);
>  u32 usb_endpoint_max_periodic_payload(struct usb_device *udev,
>  				      const struct usb_host_endpoint *ep)
>  {
> +	u32 max_payload;
> +
>  	if (!usb_endpoint_xfer_isoc(&ep->desc) &&
>  	    !usb_endpoint_xfer_int(&ep->desc))
>  		return 0;
> @@ -1135,7 +1137,12 @@ u32 usb_endpoint_max_periodic_payload(struct usb_device *udev,
>  			return le32_to_cpu(ep->ssp_isoc_ep_comp.dwBytesPerInterval);
>  		fallthrough;
>  	case USB_SPEED_SUPER:
> -		return le16_to_cpu(ep->ss_ep_comp.wBytesPerInterval);
> +		max_payload = usb_endpoint_maxp(&ep->desc) * (ep->ss_ep_comp.bMaxBurst + 1);
> +		if (usb_endpoint_xfer_isoc(&ep->desc))
> +			return max_t(u32, max_payload * USB_SS_MULT(ep->ss_ep_comp.bmAttributes),
> +					ep->ss_ep_comp.wBytesPerInterval);
> +		else
> +			return max_t(u32, max_payload, ep->ss_ep_comp.wBytesPerInterval);

You dropped the conversion from le16 to cpu?  Why?

thanks,

greg k-h