Re: at91sam9x5: USB mass storage gadget problems

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[Adding linux-usb to the CC list]

On Wed, 11 Nov 2015, Douglas Gilbert wrote:

> Hi,
> I have been running into problems trying to use a USB device port
> on an Acme System's Arietta G25 (Atmel at91sam9g25 hence at91sam9x5
> family in the kernel) as a USB mass storage gadget. Since the problem
> may be anywhere in the stack, I have sent this post to a USB expert
> as well as at91sam9x5 experts.
> 
> In all cases the mass storage device appears on the host system
> after I do 'modprobe g_mass_storage file=/tmp/backing_file' on the
> Arietta G25:
> 
> # lsscsi
> [0:0:0:0]    disk    ATA      INTEL SSDSC2BW18 DC32  /dev/sda
> [6:0:0:0]    disk    Linux    File-Stor Gadget 0400  /dev/sdb
> 
> However if the host port is USB 3.0 (e.g. on my Lenovo
> X240 laptop) and the kernel is in the 4.0 series then all attempts

You mean if the _gadget's_ kernel is >= 4.0, right?  Not the host's 
kernel.

> by the host to read data fail on that mass storage gadget.
> For example, I see lots of this in my syslog:
> 
>    sd 6:0:0:0: [sdb]
>    Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK
>    sd 6:0:0:0: [sdb] CDB:
>    Read(10): 28 00 00 00 00 00 00 00 08 00
>    end_request: I/O error, dev sdb, sector 0
>    Buffer I/O error on device sdb, logical block 0
>    usb 2-2: reset high-speed USB device number 9 using xhci_hcd
>    xhci_hcd 0000:00:14.0: xHCI xhci_drop_endpoint called with disabled ep 
> ffff8800ae58f180
>    xhci_hcd 0000:00:14.0: xHCI xhci_drop_endpoint called with disabled ep 
> ffff8800ae58f1c0
>    ...
> 
> I have tried around 6 different kernels in the lk 3.19 to lk 4.3.0
> on the mass storage gadget (Arietta) with 3.19 works while lk 4.0.0-rc4
> is the lowest (in my sample) that fails. My host system is Ubuntu 14.04
> with either its stock kernel (3.13.0-68-generic) or my own hand built
> lk 4.3.0; both react the same way to this problem.
> 
> Attached are the outputs of 'lsusb -v' for that mass storage gadget as
> seen on the host system. The "319" works while the other two fail. One
> difference is that wMaxPacketSize is 512 bytes for "319" and 64 bytes
> for the other two. Is that significant? [The block size on most
> storage devices is typically 512 bytes.]

That most certainly _is_ significant.  Almost nothing will work right
if the maxpacket size is wrong.

> Also, my problem seems to be sensitive to the host port being USB
> 3.0 since I have an older Lenovo X201 with USB 2.0 ports that does
> _not_ exhibit this problem. IOW when I connect my Arietta G25 mass
> storage gadget to the X201, it works properly for all G25 kernels
> that I have tried.
> 
> 
> Also tested a W7 host box with both USB 2.0 and USB 3.0 host ports
> and my mass storage gadget worked properly with lk 4.0.0-rc4 on
> both 2.0 and 3.0 ports. The Device Manager in W7 shows that it has
> xHCI driver present.

I don't know what's going on with Windows, but this seems like a bug in 
either the at91sam9g25 UDC driver or the composite gadget core.

Either way, your best bet for locating the bug is to continue bisecting 
between 3.19 and 4.0-rc4.  Unless someone on the mailing list has a 
better suggestion...

Alan Stern

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