From: "Bjørn Mork" bjorn@mork.no
[ Upstream commit 4d7ffcf3bf1be98d876c570cab8fc31d9fa92725 ]
A Mediatek based smartphone owner reports problems with USB tethering in Linux. The verbose USB listing shows a rndis_host interface pair (e0/01/03 + 10/00/00), but the driver fails to bind with
[ 355.960428] usb 1-4: bad CDC descriptors
The problem is a failsafe test intended to filter out ACM serial functions using the same 02/02/ff class/subclass/protocol as RNDIS. The serial functions are recognized by their non-zero bmCapabilities.
No RNDIS function with non-zero bmCapabilities were known at the time this failsafe was added. But it turns out that some Wireless class RNDIS functions are using the bmCapabilities field. These functions are uniquely identified as RNDIS by their class/subclass/protocol, so the failing test can safely be disabled. The same applies to the two types of Misc class RNDIS functions.
Applying the failsafe to Communication class functions only retains the original functionality, and fixes the problem for the Mediatek based smartphone.
Tow examples of CDC functional descriptors with non-zero bmCapabilities from Wireless class RNDIS functions are:
0e8d:000a Mediatek Crosscall Spider X5 3G Phone
CDC Header: bcdCDC 1.10 CDC ACM: bmCapabilities 0x0f connection notifications sends break line coding and serial state get/set/clear comm features CDC Union: bMasterInterface 0 bSlaveInterface 1 CDC Call Management: bmCapabilities 0x03 call management use DataInterface bDataInterface 1
and
19d2:1023 ZTE K4201-z
CDC Header: bcdCDC 1.10 CDC ACM: bmCapabilities 0x02 line coding and serial state CDC Call Management: bmCapabilities 0x03 call management use DataInterface bDataInterface 1 CDC Union: bMasterInterface 0 bSlaveInterface 1
The Mediatek example is believed to apply to most smartphones with Mediatek firmware. The ZTE example is most likely also part of a larger family of devices/firmwares.
Suggested-by: Lars Melin larsm17@gmail.com Signed-off-by: Bjørn Mork bjorn@mork.no Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/usb/cdc_ether.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
--- a/drivers/net/usb/cdc_ether.c +++ b/drivers/net/usb/cdc_ether.c @@ -206,7 +206,15 @@ int usbnet_generic_cdc_bind(struct usbne goto bad_desc; } skip: - if (rndis && header.usb_cdc_acm_descriptor && + /* Communcation class functions with bmCapabilities are not + * RNDIS. But some Wireless class RNDIS functions use + * bmCapabilities for their own purpose. The failsafe is + * therefore applied only to Communication class RNDIS + * functions. The rndis test is redundant, but a cheap + * optimization. + */ + if (rndis && is_rndis(&intf->cur_altsetting->desc) && + header.usb_cdc_acm_descriptor && header.usb_cdc_acm_descriptor->bmCapabilities) { dev_dbg(&intf->dev, "ACM capabilities %02x, not really RNDIS?\n",