Messages in this thread | | | From | Bjørn Mork <> | Subject | Re: [PATCH] net: usb: qmi_wwan: Fix for packets being rejected in the ring buffer used by the xHCI controller. | Date | Sun, 08 Mar 2020 16:26:21 +0100 |
| |
Paul Gildea <paul.gildea@gmail.com> writes:
> When MTU of modem is set to less than 1500 and a packet larger than MTU > arrives in Linux from a modem, it is discarded with -EOVERFLOW error > (Babble error). This is seen on USB3.0 and USB2.0 busses. This is > essentially because the MRU (Max Receive Size) is not a separate entity to > the MTU (Max Transmit Size) and the received packets can be larger than > those transmitted. Following the babble error there were an endless supply > of zero-length URBs which are rejected with -EPROTO (increasing the rx > input error counter each time). This is only seen on USB3.0. These continue > to come ad infinitum until the modem is shutdown, rendering the modem > unusable. There is a bug in the core USB handling code in Linux that > doesn't deal well with network MTUs smaller than 1500 bytes. By default the > dev->hard_mtu (the "real" MTU) is in lockstep with dev->rx_urb_size > (essentially an MRU), and it's the latter that is causing trouble. This has > nothing to do with the modems; the issue can be reproduced by getting a > USB-Ethernet dongle, setting the MTU to 1430, and pinging with size greater > than 1406. > > Signed-off-by: Paul Gildea <Paul.Gildea@gmail.com> > --- > drivers/net/usb/qmi_wwan.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c > index 5754bb6..545c772 100644 > --- a/drivers/net/usb/qmi_wwan.c > +++ b/drivers/net/usb/qmi_wwan.c > @@ -815,6 +815,13 @@ static int qmi_wwan_bind(struct usbnet *dev, struct > usb_interface *intf) > } > dev->net->netdev_ops = &qmi_wwan_netdev_ops; > dev->net->sysfs_groups[0] = &qmi_wwan_sysfs_attr_group; > + /* LTE Networks don't always respect their own MTU on receive side; > + * e.g. AT&T pushes 1430 MTU but still allows 1500 byte packets from > + * far-end network. Make receive buffer large enough to accommodate > + * them, and add four bytes so MTU does not equal MRU on network > + * with 1500 MTU otherwise usbnet_change_mtu() will change both. > + */ > + dev->rx_urb_size = ETH_DATA_LEN + 4; > err: > return status; > } > -- > 1.9.1
This is fine as a first step towards saner buffer handling in qmi_wwan. If real world devices use asymmetric MTUs, then we should just deal with that.
So I was going to add my ack. But the patch does not apply:
bjorn@miraculix:/usr/local/src/git/linux$ git am /tmp/l Applying: net: usb: qmi_wwan: Fix for packets being rejected in the ring buffer used by the xHCI controller. error: corrupt patch at line 10
and checkpatch says why:
bjorn@miraculix:/usr/local/src/git/linux$ scripts/checkpatch.pl /tmp/l ERROR: patch seems to be corrupt (line wrapped?) #34: FILE: drivers/net/usb/qmi_wwan.c:814: usb_interface *intf)
Could you fix up and resend? You might have to use a different email client. See https://www.kernel.org/doc/html/latest/process/email-clients.html#email-clients
Bjørn
| |