[PATCH] net: usb: cdc_mbim: add MeiG Smart SRM821 to ZLP whitelist

[Ming Wang]

The MeiG Smart SRM821 5G module (0x2dee:0x4d53) crashes and drops off
the USB bus when it receives a Zero Length Packet (ZLP) after sending
or receiving an NTB of exactly 16384 bytes (tx_max).

According to the MBIM specification, devices do not require a ZLP
if the NTB size is exactly dwNtbOutMaxSize. However, the cdc_mbim
driver defaults to sending ZLPs for devices not explicitly whitelisted
to accommodate non-conformant hardware. This default behavior breaks
the strictly conformant MeiG SRM821 module.

Add this device to the ZLP conformance whitelist (cdc_mbim_info) so
the driver will pad the NTB to avoid sending ZLPs, preventing the
device firmware from crashing.

Signed-off-by: Ming Wang <wangming01@xxxxxxxxxxx>
---
 drivers/net/usb/cdc_mbim.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/usb/cdc_mbim.c b/drivers/net/usb/cdc_mbim.c
index 877fb0ed7d3d..bf3e6af7d7c9 100644
--- a/drivers/net/usb/cdc_mbim.c
+++ b/drivers/net/usb/cdc_mbim.c
@@ -631,6 +631,10 @@ static const struct usb_device_id mbim_devs[] = {
 	  .driver_info = (unsigned long)&cdc_mbim_info,
 	},
 	/* ZLP conformance whitelist: All Ericsson MBIM devices */
+	/* MeiG Smart SRM821 ZLP conformance */
+	{ USB_DEVICE_AND_INTERFACE_INFO(0x2dee, 0x4d53, USB_CLASS_COMM, USB_CDC_SUBCLASS_MBIM, USB_CDC_PROTO_NONE),
+	  .driver_info = (unsigned long)&cdc_mbim_info,
+	},
 	{ USB_VENDOR_AND_INTERFACE_INFO(0x0bdb, USB_CLASS_COMM, USB_CDC_SUBCLASS_MBIM, USB_CDC_PROTO_NONE),
 	  .driver_info = (unsigned long)&cdc_mbim_info,
 	},
-- 
2.43.7