netdev - RE: [PATCH net 1/2] r8152: fix the sw rx checksum is unavailable

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Message-ID: <0835B3720019904CB8F7AA43166CEEB20105653D@RTITMBSV03.realtek.com.tw>
Date:   Fri, 25 Nov 2016 09:52:20 +0000
From:   Hayes Wang <hayeswang@...ltek.com>
To:     Mark Lord <mlord@...ox.com>, Greg KH <greg@...ah.com>
CC:     David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        nic_swsd <nic_swsd@...ltek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: RE: [PATCH net 1/2] r8152: fix the sw rx checksum is unavailable

Mark Lord [mailto:mlord@...ox.com]
> Sent: Friday, November 25, 2016 3:11 AM
[...]
> On 16-11-24 02:00 PM, Greg KH wrote:
> > On Thu, Nov 24, 2016 at 01:34:08PM -0500, Mark Lord wrote:
> >> One thought:  bulk data streams are byte streams, not packets.
> >> Scheduling on the USB bus can break up larger transfers across
> >> multiple in-kernel buffers.  A "real" URB buffer on USB2 is max 512 bytes.
> >> The driver is providing 16384-byte buffers, and assumes that data will
> >> never spill over from one such buffer to the next.
> >> Yet the observations here consistently show otherwise.
> >
> > Wait, how do you know that data will not spill over?  What is making
> > that guarantee?  Will the USB device send a "zero packet" in order to
> > show that all of the "logical" data is now sent for this specific
> > endpoint?  Is there some sort of "framing" that the device does with the
> > USB data so that the driver "knows" where the end of packet is?
> 
> Exactly my point.
> 
> > Check the zero-packet stuff for this device, that's tripped up many a
> > USB driver writer over the years, myself included.
> 
> I haven't tripped over it myself, but only because we were careful
> to allow for such in the USB drivers I have worked on.
> 
> The r8152 driver just assumes it never happens.

What is the value of /sys/bus/usb/devices/.../power/control ?
Could you make sure it is "on" and try again?
Or you could call usb_disable_autosuspend() in probe().

Best Regards,
Hayes