> On Wed, Sep 11, 2013 at 8:56 PM, David Laight <David.Laight@xxxxxxxxxx> wrote: > >> > > 2) If 'length % dev->maxpacket == 0' for a multi-fragment packet then > >> > > the extra byte isn't added correctly (the code probably falls off > >> > > the end of the scatter-gather list). > >> > > >> > Indeed. Ming Lei, should usbnet handle this in the sg case or better > >> > leave it to the subdriver you introduced this for? > > > > Is the ZLP issue a problem with the host or with the target? > > Sorry, what do you mean the ZLP issue here? I understand Oliver > thinks one commit from me may break ZLP handling, are you discussing > this problem? If not, could you explain it in a bit detail? I was thinking of the general ZLP problem. > > If it is a host problem then the necessity comes from the host, > > but the fix needs to be target dependant. > > If it is a common target problem then generic code can apply > > a common fix. > > All usbnet device should have sent one ZLP in case the size of > bulk out transfer can be divided by max packet size, but the one > byte transfer might be introduced for avoiding some target problem > (can't deal with zlp well), as said by David, see below discussion: > > http://marc.info/?l=linux-usb&m=127067487604112&w=2 AFAICT the code avoids sending a zero length packet (that would terminate a USB bulk transfer packet) by increasing the length of the bulk packet by (at least) one byte. > > AFICT there are at least 3 fixes: > > 1) Extend the ethernet frame by one byte and hope the receiving > > system doesn't object to the padding. > > This is probably the only option if tx_fixup() doesn't > > add a header. > > 2) Put the ethernet frame length in the header and have the > > target discard the added pad byte (ax88179_178a.c). > > 3) Add a second zero-length frame in the same USB data block > > (ax88172a.c). > > Why do we need the above 3 fixes? The patch in my last email can > fix the problem which is introduced recently, can't it? I meant there are 3 ways of avoiding the ZLP, each driver will pick one of them. I've just looked at all the drivers in net/usb. It doesn't look like they all handle fragmented skb, shared skb, or ZLP properly. A lot of common code could be removed if usbnet knew the size of the header and allocated it before calling tx_fixup(). None of this is helping me sort out why netperf udp rr tests with burst 19 are losing all the packets at once :-( David -- 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
