[U-Boot] [EXT][xhci] XHCI Short Packet Issues

Aaron Williams awilliams at marvell.com
Mon Sep 9 23:53:21 UTC 2019

Hi Bin,

I have some more data. It looks like U-Boot is not properly handling the short 
transfer case according to section in the XHCI 3.1 specification. 
In this case, when the data fits in the first TRB, two transfer event TRBs 
will be generated. The first one will indicate that there is a short packet 
and points to the first TRB and the length is calculated based on the TRB 
pointed to, not the total TRB. A second success TRB is also received.

This seems consistent with what I am seeing. U-Boot does not handle this at 
all. It expects there to always be a single transfer event TRB with the length 
calculated based on the total length, not the TRB length. I can re-work this 
so that short packets can be better handled. 

The easiest way to test this is with a USB Ethernet dongle then modifying 
drivers/usb/eth/usb_ether.c to force it to allocate a buffer that will span 
64K where packets fit in the first half. I have attached this patch to force 
the XHCI problem to manifest itself.


On Friday, July 12, 2019 8:51:41 PM PDT Aaron Williams wrote:
> No, it's our Marvell OcteonTX2 SoC. I put in what I thought was a fix, but
> I'm still working on it. This issue only shows up when using a USB Ethernet
> device where the rx buffer crosses a 64K boundary and the packet is
> received in the first buffer. I don't know how other hardware behaves in
> this situation. The case I'm seeing this is where the receive buffer starts
> at 128 bytes away from a 64K boundary so two receive TRBs are used. The
> first is for 128 bytes and the other is for the rest of the buffer. This is
> with the asix88179.
> I am seeing some other strange behavior which is leading me to believe there
> may be some underlying hardware issue which I am looking into. In my case
> I'm seeing the transfer event response length with a short packet (13)
> saying it's 48 bytes (the size of the ARP packet) instead of 5K - 48 which
> is what it looks like the code expects.
> I am in contact now with one of our hardware designers who can hopefully
> answer what's going on.
> -Aaron
> From: Bin Meng <bmeng.cn at gmail.com>
> Sent: Wednesday, July 10, 2019 9:57 PM
> To: Aaron Williams
> Cc: u-boot at lists.denx.de
> Subject: [EXT] Re: [U-Boot] [u-boot][xhci] Dealing with XHCI controllers
> with spurious success
> External Email
> ----------------------------------------------------------------------
> Hi Aaron,
> On Thu, Jul 11, 2019 at 12:50 PM Aaron Williams <awilliams at marvell.com> 
> > Hi All,
> > 
> > 
> > 
> > I'm running into a problem with the XHCI driver on our SOC where I am
> > getting spurious success TRBs after a short packet response. In this
> > particular case, the driver for a USB network controller has a receive
> > buffer that crosses a 64K boundary. This results
>  in two TRBs being created to handle this with the first TRB having the
> chain and ISP bits set and the second having the IOC and ISP bits set as
> expected in this case.
> > The network controller has a short response (as is expected) followed by a
> > success response event (which is also valid) for the second TRB.  The
> > U-Boot XHCI driver, however, does not handle this properly. The
> > xhci_bulk_tx function only looks at the first
>  response and does not dequeue the second success response. The problem is
> when the next transaction occurs it dequeues the success response from the
> previous transaction so the responses events no longer match the TRBs. At
> some point the network driver goes from receive to transmit and at this
> point the driver panics because the event is still a response from a
> previous receive event and not the transmit event causing the endpoints to
> mismatch. This only happens in the two TRB case due to the receive buffer
> crossing a 64K boundary. The short packet response points to the first TRB
> and the success points to the second TRB.
> > In the Linux driver I see the XHCI_SPURIOUS_SUCCESS flag is available. I'm
> > not certain if this applies to our hardware or not. In any case, this
> > could be solved in one of two ways. One way to solve this is to make sure
> > that any driver where a short response
>  is possible to not have the buffer cross a 64K boundary. The other (and
> correct) solution is to have the XHCI driver handle this case. If a short
> packet response is received and there are multiple TRBs involved, check if
> there is an additional success response that points to the last TRB.
> > To me it seems valid that the two response events are received. The
> > specification only says that there will be one response if the TRB has
> > both the ISP and IOC bits set, but this is not the case. I came across
> > this commit in the Linux kernel which seems to
>  address this case:
> https://kernel.opensuse.org/cgit/kernel/commit/?id=ad808333d8201d53075a11bc8
> dd83b81f3d68f0b
> Are you using an Intel SoC? From the commit you gave, it looks it only
> applies to a specific Intel PCH chipset.
> Regards,
> Bin
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> https://lists.denx.de/listinfo/u-boot

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