Re: [Qemu-devel] [PATCH v2 2/2] e1000: decrement RDT if equal to RDH

[Jason Wang <jasowang@redhat.com>]

----- Original Message -----
> Some drivers set RDT=RDH. Oddly, this works on real hardware. To work
> around this, autodecrement RDT when this happens.
> 
> Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
> Signed-off-by: Jeff Westfahl <jeff.westfahl@ni.com>
> ---
>  hw/net/e1000.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Please describe more details on the issue.

The spec 3.2.6 said:

"
When the head pointer is equal to the tail pointer, the ring is empty. 
"

So RDT=RDH in fact empty the ring. No?
> 
> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
> index 44ae3a8..b8cbfc1 100644
> --- a/hw/net/e1000.c
> +++ b/hw/net/e1000.c
> @@ -1152,6 +1152,12 @@ mac_writereg(E1000State *s, int index, uint32_t val)
>  static void
>  set_rdt(E1000State *s, int index, uint32_t val)
>  {
> +    if (val == s->mac_reg[RDH]) {     /* Decrement RDT if it's too big */
> +        if (val == 0) {
> +            val = s->mac_reg[RDLEN] / sizeof(struct e1000_rx_desc);
> +        }
> +        val--;
> +    }
>      s->mac_reg[index] = val & 0xffff;
>      if (e1000_has_rxbufs(s, 1)) {
>          qemu_flush_queued_packets(qemu_get_queue(s->nic));
> --
> 2.1.3
> 
> 
>