On Sun, Jul 06, 2014 at 09:26:02PM +0500, Abbas Raza wrote: > From: Abbas Raza <Abbas_Raza@xxxxxxxxxx> > > 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@xxxxxxxxxx> > --- > drivers/usb/chipidea/udc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c > index 7a12d13..2857dff 100644 > --- a/drivers/usb/chipidea/udc.c > +++ b/drivers/usb/chipidea/udc.c > @@ -1169,8 +1169,8 @@ static int ep_enable(struct usb_ep *ep, > > if (hwep->type == USB_ENDPOINT_XFER_CONTROL) > cap |= QH_IOS; > - if (hwep->num) > - cap |= QH_ZLT; > + > + cap |= QH_ZLT; > cap |= (hwep->ep.maxpacket << __ffs(QH_MAX_PKT)) & QH_MAX_PKT; > /* > * For ISO-TX, we set mult at QH as the largest value, and use > -- > 1.8.3.2 > Good fix, I will apply it after testing, thanks. -- Best Regards, Peter Chen -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
