mirror of https://gitee.com/openkylin/linux.git
953c664697
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. Cc: stable@vger.kernel.org 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> |
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.. | ||
Kconfig | ||
Makefile | ||
bits.h | ||
ci.h | ||
ci_hdrc_imx.c | ||
ci_hdrc_imx.h | ||
ci_hdrc_msm.c | ||
ci_hdrc_pci.c | ||
ci_hdrc_zevio.c | ||
core.c | ||
debug.c | ||
debug.h | ||
host.c | ||
host.h | ||
otg.c | ||
otg.h | ||
otg_fsm.c | ||
otg_fsm.h | ||
udc.c | ||
udc.h | ||
usbmisc_imx.c |