Re: [PATCH net v6 4/4] tg3: Fix tx_pending checks for tg3_tso_bug

Eric Dumazet
2014-10-01T04:24:51Z

On Tue, 2014-09-30 at 20:14 -0700, Prashant wrote:

> Sorry about the late reply, out of all the HW bug conditions checked in
> tg3_tx_frag_set() the most frequently hit condition is the short 8 byte
> dma bug, where the chip cannot handle TX descriptors whose data buffer
> is 8 bytes or less. Most of the LSO skb's given to the driver has their
> fragments filled upto PAGE_SIZE (expect the last fragment depending on
> skb->len). And if such a LSO skb's last fragment meets the 8 bytes HW
> bug condition the above routine will not help workaround this particular
> case.

Thats pretty easy to work around.

Say rebuilt skb has N frags (N > 1 given your description)

They are numbered 0, ... N-2, N-1

Instead of filling N-2 completely, fill it to PAGE_SIZE-8, so that last
frag has at least 8 bytes in it.

Also take a look at commit 2e4e44107176d552f8bb1bb76053e850e3809841
("net: add alloc_skb_with_frags() helper")