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

[Michal Pecio]

On Thu, 2 Apr 2026 19:55:16 +0800, Xuetao (kirin) wrote:
> > Any other examples besides AX88179?  
> 
> We tested 18 different USB 3.0 docks, but they only contained two 
> different types of USB 3.0 Ethernet devices based on VID/PID.
> The dwc3 controller works fine with all of the devices mentioned
> above. The other USB host controller works fine with all 12 Realtek
> devices, but fails with all 6 ASIX devices.
> 
> 1. Realtek USB 10/100/1000 LAN (12 devices)
> All 12 devices share the same VID/PID and descriptor values.
> 
> VID = 0x0BDA, PID = 0x8153
> wMaxPacketSize = 0x10
> bMaxBurst = 0
> wBytesPerInterval = 0x8

My RTL8153 has this endpoint for its default proprietary configuration:

        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0002  1x 2 bytes
        bInterval               8
        bMaxBurst               0
        wBytesPerInterval       2

which should be problem-free, and this for its CDC configuration:

        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0010  1x 16 bytes
        bInterval               8
        bMaxBurst               0
        wBytesPerInterval       8

The CDC configuration needs to be enabled with a patch, I'm not sure
if there is any other way. It will then use the r8153_ecm driver.

--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -9641,6 +9641,7 @@ static int rtl_fw_init(struct r8152 *tp)
 
 static u8 __rtl_get_hw_ver(struct usb_device *udev)
 {
+	return 0;
 	u32 ocp_data = 0;
 	__le32 *tmp;
 	u8 version;

> 2. ASIX AX88179 USB 3.0 to Gigabit Ethernet Adapter (6 devices)
> All 6 devices share the same VID/PID.
> 
> VID = 0x0B95, PID = 0x1790
> (a) 4 devices:
> wMaxPacketSize = 0x10
> bMaxBurst = 0
> wBytesPerInterval = 0x0

This looks like my AX88179 and it's obviously broken.

> (b) 2 devices:
> wMaxPacketSize = 0x10
> bMaxBurst = 0
> wBytesPerInterval = 0x8

But this is odd. When I use mine, I see that the driver submits 8 byte
URBs and they complete successfully with 8 bytes received, no babble.

ffff888100981b40 3364969734 S Ii:2:010:1 -115:1024 8 <
ffff888100981b40 3365097706 C Ii:2:010:1 0:1024 8 = a1000800 79490000

So I think this should work even with bandwidth reservation set to 8.
Can you check what happens here, before and after your patch?

Regards,
Michal