[PATCH net v2] net: usb: cdc_ncm: add Apple Silicon MacBook Air (05ac:1903) device ID

[Divyanshu Jha]

The Apple Silicon MacBook Air exposes a CDC-NCM interface (05ac:1903)
when connected host-to-host over USB-C.

The device tested is an Apple MacBook Air (13-inch, M1, 2020), Model A2337
(MacBookAir10,1) with an Apple M1 chip. Unlike
commit a5148bc2fa27 ("net: usb: cdc_ncm: add Apple Mac USB-C direct networking quirk")
which hypothesized all Apple Silicon Macs share PID 0x1905 ("Mac"), this
M1 MacBook Air exposes PID 0x1903 with iProduct string "MacBook Air".

Like other Apple CDC-NCM peripherals (0x1902 and 0x1905), Apple's
firmware omits the CDC status interrupt endpoint. This causes the
standard cdc_ncm probe to fail with a missing endpoint error:

  cdc_ncm 1-7:1.0: bind() failure
  cdc_ncm: probe of 1-7:1.0 failed with error -22

Add device ID 05ac:1903 to cdc_devs binding to
apple_private_interface_info so the driver bypasses the interrupt
check and initializes host-to-host networking successfully:

  cdc_ncm 1-7:1.0 usb0: register 'cdc_ncm' at usb-...,
  CDC NCM (Apple Private), ...

Relevant 'lsusb -v' descriptor output:

  Device Descriptor:
    bcdUSB               2.10
    idVendor           0x05ac Apple, Inc.
    idProduct          0x1903 MacBook Air
    bcdDevice           10.01
    iManufacturer           1 Apple Inc.
    iProduct                2 MacBook Air
    Configuration Descriptor:
      Interface Descriptor:
        bInterfaceNumber        0
        bInterfaceClass         2 Communications
        bInterfaceSubClass     13 CDC NCM
        bNumEndpoints           0
      Interface Descriptor:
        bInterfaceNumber        1
        bInterfaceClass        10 CDC Data
        bNumEndpoints           2
      Interface Descriptor:
        bInterfaceNumber        2
        bInterfaceClass         2 Communications
        bInterfaceSubClass     13 CDC NCM
        bNumEndpoints           0
      Interface Descriptor:
        bInterfaceNumber        3
        bInterfaceClass        10 CDC Data
        bNumEndpoints           2

Reviewed-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>
Signed-off-by: Divyanshu Jha <divyanshuj2006@xxxxxxxxx>
---
v1 -> v2:
- Retarget from net-next to net.
- Clarify hardware model (MacBook Air M1 2020, A2337) and contrast with
  commit a5148bc2fa27.
- Add 'lsusb -v' descriptor output and dmesg failure/success logs.
- Fix typo in commit message: cdc_ncm_devs -> cdc_devs.
- Add Reviewed-by tag from Nicolai Buchwitz.
- Link to v1: https://lore.kernel.org/netdev/20261023070419.235361-1-divyanshuj2006@xxxxxxxxx/

 drivers/net/usb/cdc_ncm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 35db38cb3e4a..6848b9421137 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -2019,6 +2019,12 @@ static const struct usb_device_id cdc_devs[] = {
 	{ USB_DEVICE_INTERFACE_NUMBER(0x05ac, 0x1902, 2),
 		.driver_info = (unsigned long)&apple_private_interface_info,
 	},
+	{ USB_DEVICE_INTERFACE_NUMBER(0x05ac, 0x1903, 0),
+		.driver_info = (unsigned long)&apple_private_interface_info,
+	},
+	{ USB_DEVICE_INTERFACE_NUMBER(0x05ac, 0x1903, 2),
+		.driver_info = (unsigned long)&apple_private_interface_info,
+	},
 	{ USB_DEVICE_INTERFACE_NUMBER(0x05ac, 0x1905, 0),
 		.driver_info = (unsigned long)&apple_private_interface_info,
 	},
-- 
2.47.3