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linux/drivers/usb
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Abbas Raza 3b5e2408ca usb: chipidea: udc: Disable auto ZLP generation on ep0 
commit 953c664697 upstream.

There are 2 methods for ZLP (zero-length packet) generation:
1) In software
2) Automatic generation by device controller

1) is implemented in UDC driver and it attaches ZLP to IN packet if
   descriptor->size < wLength
2) can be enabled/disabled by setting ZLT bit in the QH

When gadget ffs is connected to ubuntu host, the host sends
get descriptor request and wLength in setup packet is 255 while the
size of descriptor which will be sent by gadget in IN packet is
64 byte. So the composite driver sets req->zero = 1.
In UDC driver following code will be executed then

        if (hwreq->req.zero && hwreq->req.length
            && (hwreq->req.length % hwep->ep.maxpacket == 0))
                add_td_to_list(hwep, hwreq, 0);

Case-A:
So in case of ubuntu host, UDC driver will attach a ZLP to the IN packet.
ubuntu host will request 255 byte in IN request, gadget will send 64 byte
with ZLP and host will come to know that there is no more data.
But hold on, by default ZLT=0 for endpoint 0 so hardware also tries to
automatically generate the ZLP which blocks enumeration for ~6 seconds due
to endpoint 0 STALL, NAKs are sent to host for any requests (OUT/PING)

Case-B:
In case when gadget ffs is connected to Apple device, Apple device sends
setup packet with wLength=64. So descriptor->size = 64 and wLength=64
therefore req->zero = 0 and UDC driver will not attach any ZLP to the
IN packet. Apple device requests 64 bytes, gets 64 bytes and doesn't
further request for IN data. But ZLT=0 by default for endpoint 0 so
hardware tries to automatically generate the ZLP which blocks enumeration
for ~6 seconds due to endpoint 0 STALL, NAKs are sent to host for any
requests (OUT/PING)

According to USB2.0 specs:

    8.5.3.2 Variable-length Data Stage
    A control pipe may have a variable-length data phase in which the
    host requests more data than is contained in the specified data
    structure. When all of the data structure is returned to the host,
    the function should indicate that the Data stage is ended by
    returning a packet that is shorter than the MaxPacketSize for the
    pipe. If the data structure is an exact multiple of wMaxPacketSize
    for the pipe, the function will return a zero-length packet to indicate
    the end of the Data stage.

In Case-A mentioned above:
If we disable software ZLP generation & ZLT=0 for endpoint 0 OR if software
ZLP generation is not disabled but we set ZLT=1 for endpoint 0 then
enumeration doesn't block for 6 seconds.

In Case-B mentioned above:
If we disable software ZLP generation & ZLT=0 for endpoint then enumeration
still blocks due to ZLP automatically generated by hardware and host not needing
it. But if we keep software ZLP generation enabled but we set ZLT=1 for
endpoint 0 then enumeration doesn't block for 6 seconds.

So the proper solution for this issue seems to disable automatic ZLP generation
by hardware (i.e by setting ZLT=1 for endpoint 0) and let software (UDC driver)
handle the ZLP generation based on req->zero field.

Signed-off-by: Abbas Raza <Abbas_Raza@mentor.com>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2014-07-28 08:05:56 -07:00
..
atm usb: delete non-required instances of include <linux/init.h> 2014-01-08 15:01:39 -08:00
c67x00 USB: c67x00: correct spelling mistakes in comments 2014-01-08 15:05:14 -08:00
chipidea usb: chipidea: udc: Disable auto ZLP generation on ep0 2014-07-28 08:05:56 -07:00
class USB: cdc-acm: fix runtime PM imbalance at shutdown 2014-06-26 15:15:41 -04:00
core usb: Check if port status is equal to RxDetect 2014-07-28 08:05:56 -07:00
dwc2 usb: dwc2: fix memory corruption in dwc2 driver 2014-02-04 12:59:14 -08:00
dwc3 usb: dwc3: gadget: clear stall when disabling endpoint 2014-06-30 20:11:53 -07:00
early USB: ehci-dbgp: drop dead code. 2013-09-26 16:25:21 -07:00
gadget usb: gadget: f_fs: fix NULL pointer dereference when there are no strings 2014-07-09 11:18:24 -07:00
host xhci: Fix runtime suspended xhci from blocking system suspend. 2014-07-09 11:18:23 -07:00
image USB: image: correct spelling mistake in comment 2014-01-08 15:08:14 -08:00
misc USB: usbtest: add a timeout for scatter-gather tests 2014-06-30 20:11:52 -07:00
mon USB: regroup all depends on USB within an if USB block 2013-04-09 16:49:07 -07:00
musb usb: musb: Fix panic upon musb_am335x module removal 2014-07-09 11:18:24 -07:00
phy ARM: OMAP: replace checks for CONFIG_USB_GADGET_OMAP 2014-06-30 20:11:53 -07:00
renesas_usbhs usb: changes for v3.14 merge window 2014-01-03 12:15:10 -08:00
serial USB: serial: ftdi_sio: Add Infineon Triboard 2014-07-17 16:21:02 -07:00
storage USB: Nokia 5300 should be treated as unusual dev 2014-06-07 10:28:16 -07:00
wusbcore usb: delete non-required instances of include <linux/init.h> 2014-01-08 15:01:39 -08:00
Kconfig USB patches for 3.14-rc1 2014-01-20 16:13:02 -08:00
Makefile Move DWC2 driver out of staging 2014-01-13 14:44:01 -08:00
README USB: fix directory references in usb/README 2007-11-28 13:58:34 -08:00
usb-common.c usb: common: introduce of_usb_get_maximum_speed() 2013-07-29 13:56:46 +03:00
usb-skeleton.c usb: delete non-required instances of include <linux/init.h> 2014-01-08 15:01:39 -08:00

README 

To understand all the Linux-USB framework, you'll use these resources:

    * This source code.  This is necessarily an evolving work, and
      includes kerneldoc that should help you get a current overview.
      ("make pdfdocs", and then look at "usb.pdf" for host side and
      "gadget.pdf" for peripheral side.)  Also, Documentation/usb has
      more information.

    * The USB 2.0 specification (from www.usb.org), with supplements
      such as those for USB OTG and the various device classes.
      The USB specification has a good overview chapter, and USB
      peripherals conform to the widely known "Chapter 9".

    * Chip specifications for USB controllers.  Examples include
      host controllers (on PCs, servers, and more); peripheral
      controllers (in devices with Linux firmware, like printers or
      cell phones); and hard-wired peripherals like Ethernet adapters.

    * Specifications for other protocols implemented by USB peripheral
      functions.  Some are vendor-specific; others are vendor-neutral
      but just standardized outside of the www.usb.org team.

Here is a list of what each subdirectory here is, and what is contained in
them.

core/		- This is for the core USB host code, including the
		  usbfs files and the hub class driver ("khubd").

host/		- This is for USB host controller drivers.  This
		  includes UHCI, OHCI, EHCI, and others that might
		  be used with more specialized "embedded" systems.

gadget/		- This is for USB peripheral controller drivers and
		  the various gadget drivers which talk to them.


Individual USB driver directories.  A new driver should be added to the
first subdirectory in the list below that it fits into.

image/		- This is for still image drivers, like scanners or
		  digital cameras.
../input/	- This is for any driver that uses the input subsystem,
		  like keyboard, mice, touchscreens, tablets, etc.
../media/	- This is for multimedia drivers, like video cameras,
		  radios, and any other drivers that talk to the v4l
		  subsystem.
../net/		- This is for network drivers.
serial/		- This is for USB to serial drivers.
storage/	- This is for USB mass-storage drivers.
class/		- This is for all USB device drivers that do not fit
		  into any of the above categories, and work for a range
		  of USB Class specified devices. 
misc/		- This is for all USB device drivers that do not fit
		  into any of the above categories.