RE: [PATCH net-next v26 07/13] rtase: Implement a function to receive packets

[Justin Lai]

> On Wed, 7 Aug 2024 11:37:17 +0800 Justin Lai wrote:
> > +static int rx_handler(struct rtase_ring *ring, int budget) {
> > +     union rtase_rx_desc *desc_base = ring->desc;
> > +     u32 pkt_size, cur_rx, delta, entry, status;
> > +     struct rtase_private *tp = ring->ivec->tp;
> > +     struct net_device *dev = tp->dev;
> > +     union rtase_rx_desc *desc;
> > +     struct sk_buff *skb;
> > +     int workdone = 0;
> > +
> > +     cur_rx = ring->cur_idx;
> > +     entry = cur_rx % RTASE_NUM_DESC;
> > +     desc = &desc_base[entry];
> > +
> > +     do {
> > +             /* make sure discriptor has been updated */
> > +             dma_rmb();
> 
> I think I already asked, but this still makes no sense to me.
> dma barriers are between accesses to descriptors.
> dma_rmb() ensures ordering of two reads.
> Because modern CPUs can perform reads out of order.
> What two reads is this barrier ordering?
> 
> Please read the doc on memory barriers relating to dma.
> I think this is in the wrong place.
> 
> r8169 gets it right.

Thank you for your reply. I will modify it.

Thanks
Justin
> 
> > +             status = le32_to_cpu(desc->desc_status.opts1);
> > +
> > +             if (status & RTASE_DESC_OWN)
> > +                     break;
> > +