linux-kernel - Re: [PATCH] usbnet: ipheth: fix connectivity with iOS 14

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Date:   Sun, 21 Feb 2021 10:42:44 +0000
From:   Sam Bingner <sam@...gner.com>
To:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
CC:     "David S. Miller" <davem@...emloft.net>,
        Martin Habets <mhabets@...arflare.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Shannon Nelson <snelson@...sando.io>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Matti Vuorela <matti.vuorela@...factor.fi>,
        Jakub Kicinski <kuba@...nel.org>,
        "Yves-Alexis Perez" <corsac@...sac.net>
Subject: Re: [PATCH] usbnet: ipheth: fix connectivity with iOS 14

There seems to be a problem with this patch:

Whenever the iPhone sends a packet to the tethered device that is 1500 bytes long, it gets the error "ipheth 1-1:4.2: ipheth_rcvbulk_callback: urb status: -79" on the connected device and stops passing traffic.  I am able to bring it back up by shutting and unshutting the interface, but the same thing happens very quickly.   I noticed that this patch dropped the max USB packet size from 1516 to 1514 bytes, so I decided to try lowering the MTU to 1498; this made the connection reliable and no more errors occurred.

It appears to me that the iPhone is still sending out 1516 bytes over USB for a 1500 byte packet and this patch makes USB abort when that happens?  I could duplicate reliably by sending a ping from the iphone (ping -s 1472) to the connected device, or vice versa as the reply would then break it.

I apologize if this reply doesn't end up where it should - I tried to reply to the last message in this thread but I wasn't actually *on* the thread so I had to just build it as much as possible myself.

Sam