On Sun, Feb 4, 2024 at 11:47 PM Krishna Kurapati quic_kriskura@quicinc.com wrote:
It is observed sometimes when tethering is used over NCM with Windows 11 as host, at some instances, the gadget_giveback has one byte appended at the end of a proper NTB. When the NTB is parsed, unwrap call looks for any leftover bytes in SKB provided by u_ether and if there are any pending bytes, it treats them as a separate NTB and parses it. But in case the second NTB (as per unwrap call) is faulty/corrupt, all the datagrams that were parsed properly in the first NTB and saved in rx_list are dropped.
Adding a few custom traces showed the following: [002] d..1 7828.532866: dwc3_gadget_giveback: ep1out: req 000000003868811a length 1025/16384 zsI ==> 0 [002] d..1 7828.532867: ncm_unwrap_ntb: K: ncm_unwrap_ntb toprocess: 1025 [002] d..1 7828.532867: ncm_unwrap_ntb: K: ncm_unwrap_ntb nth: 1751999342 [002] d..1 7828.532868: ncm_unwrap_ntb: K: ncm_unwrap_ntb seq: 0xce67 [002] d..1 7828.532868: ncm_unwrap_ntb: K: ncm_unwrap_ntb blk_len: 0x400 [002] d..1 7828.532868: ncm_unwrap_ntb: K: ncm_unwrap_ntb ndp_len: 0x10 [002] d..1 7828.532869: ncm_unwrap_ntb: K: Parsed NTB with 1 frames
In this case, the giveback is of 1025 bytes and block length is 1024. The rest 1 byte (which is 0x00) won't be parsed resulting in drop of all datagrams in rx_list.
Same is case with packets of size 2048: [002] d..1 7828.557948: dwc3_gadget_giveback: ep1out: req 0000000011dfd96e length 2049/16384 zsI ==> 0 [002] d..1 7828.557949: ncm_unwrap_ntb: K: ncm_unwrap_ntb nth: 1751999342 [002] d..1 7828.557950: ncm_unwrap_ntb: K: ncm_unwrap_ntb blk_len: 0x800
Lecroy shows one byte coming in extra confirming that the byte is coming in from PC:
Transfer 2959 - Bytes Transferred(1025) Timestamp((18.524 843 590)
- Transaction 8391 - Data(1025 bytes) Timestamp(18.524 843 590)
--- Packet 4063861 Data(1024 bytes) Duration(2.117us) Idle(14.700ns) Timestamp(18.524 843 590) --- Packet 4063863 Data(1 byte) Duration(66.160ns) Time(282.000ns) Timestamp(18.524 845 722)
According to Windows driver, no ZLP is needed if wBlockLength is non-zero, because the non-zero wBlockLength has already told the function side the size of transfer to be expected. However, there are in-market NCM devices that rely on ZLP as long as the wBlockLength is multiple of wMaxPacketSize. To deal with such devices, it pads an extra 0 at end so the transfer is no longer multiple of wMaxPacketSize.
Cc: stable@vger.kernel.org Fixes: 9f6ce4240a2b ("usb: gadget: f_ncm.c added") Signed-off-by: Krishna Kurapati quic_kriskura@quicinc.com
Link to v2: https://lore.kernel.org/all/20240131150332.1326523-1-quic_kriskura@quicinc.c...
Changes in v2: Added check to see if the padded byte is 0x00.
Changes in v3: Removed wMaxPacketSize check from v2.
drivers/usb/gadget/function/f_ncm.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c index ca5d5f564998..e2a059cfda2c 100644 --- a/drivers/usb/gadget/function/f_ncm.c +++ b/drivers/usb/gadget/function/f_ncm.c @@ -1338,7 +1338,15 @@ static int ncm_unwrap_ntb(struct gether *port, "Parsed NTB with %d frames\n", dgram_counter);
to_process -= block_len;
if (to_process != 0) {
/** Windows NCM driver avoids USB ZLPs by adding a 1-byte* zero pad as needed.*/if (to_process == 1 &&(*(unsigned char *)(ntb_ptr + block_len) == 0x00)) {to_process--;} else if (to_process > 0) { ntb_ptr = (unsigned char *)(ntb_ptr + block_len); goto parse_ntb; }-- 2.34.1
Reviewed-by: Maciej Żenczykowski maze@google.com
Let's get this fix out.
Greg, there's further code cleanups (here and elsewhere) I'll send once this is merged. I don't want to annoy Krishna further ;-)