On 10-02-26 04:38 PM, Anton Vorontsov wrote: > OK, I think I found what's happening in gianfar. > > Some background... > > start_xmit() prepares new skb for transmitting, generally it does > three things: > > 1. sets up all BDs (marks them ready to send), except the first one. > 2. stores skb into tx_queue->tx_skbuff so that clean_tx_ring() > would cleanup it later. > 3. sets up the first BD, i.e. marks it ready. > > Here is what clean_tx_ring() does: > > 1. reads skbs from tx_queue->tx_skbuff > 2. Checks if the *last* BD is ready. If it's still ready [to send] > then it it isn't transmitted, so clean_tx_ring() returns. > Otherwise it actually cleanups BDs. All is OK. > > Now, if there is just one BD, code flow: > > - start_xmit(): stores skb into tx_skbuff. Note that the first BD > (which is also the last one) isn't marked as ready, yet. > - clean_tx_ring(): sees that skb is not null, *and* its lstatus > says that it is NOT ready (like if BD was sent), so it cleans > it up (bad!) > - start_xmit(): marks BD as ready [to send], but it's too late. > > We can fix this simply by reordering lstatus/tx_skbuff writes. > > It works flawlessly on my p2020, please try it.
I've skipped right to the test part (I'll think about the description more later) and it passed 5 out of 5 boot tests on NFSroot sbc8641d. Looks like you've got a solution. Paul. > > Thanks! > > > diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c > index 8bd3c9f..cccb409 100644 > --- a/drivers/net/gianfar.c > +++ b/drivers/net/gianfar.c > @@ -2021,7 +2021,6 @@ static int gfar_start_xmit(struct sk_buff *skb, struct > net_device *dev) > } > > /* setup the TxBD length and buffer pointer for the first BD */ > - tx_queue->tx_skbuff[tx_queue->skb_curtx] = skb; > txbdp_start->bufPtr = dma_map_single(&priv->ofdev->dev, skb->data, > skb_headlen(skb), DMA_TO_DEVICE); > > @@ -2053,6 +2052,10 @@ static int gfar_start_xmit(struct sk_buff *skb, struct > net_device *dev) > > txbdp_start->lstatus = lstatus; > > + eieio(); /* force lstatus write before tx_skbuff */ > + > + tx_queue->tx_skbuff[tx_queue->skb_curtx] = skb; > + > /* Update the current skb pointer to the next entry we will use > * (wrapping if necessary) */ > tx_queue->skb_curtx = (tx_queue->skb_curtx + 1)& _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
