Re: [Qemu-devel] [PATCH 2/2] net: Fix lan9118 buffer length handling

[Peter Crosthwaite]

On Sat, Dec 21, 2013 at 4:26 AM, Roy Franz <address@hidden> wrote:
> The 9118 ethernet controller supports transmission of multi-buffer packets
> with arbitrary byte alignment of the start and end bytes.  All writes to
> the packet fifo are 32 bits, so the controller discards bytes at the beginning
> and end of each buffer based on the 'Data start offset' and 'Buffer size'
> of the TX command 'A' format.
>
> This patch uses the provided buffer length to limit the bytes transmitted.
> Previously all the bytes of the last 32-bit word written to the TX fifo
> were added to the internal transmit buffer structure resulting in more bytes
> being transmitted than were submitted to the hardware in the command.  This
> resulted in extra bytes being inserted into the middle of multi-buffer
> packets when the non-final buffers had non-32bit aligned ending addresses.
>
> Signed-off-by: Roy Franz <address@hidden>
> ---
>  hw/net/lan9118.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/hw/net/lan9118.c b/hw/net/lan9118.c
> index c5d6f14..712bb41 100644
> --- a/hw/net/lan9118.c
> +++ b/hw/net/lan9118.c
> @@ -773,11 +773,10 @@ static void tx_fifo_push(lan9118_state *s, uint32_t val)
>                 in FIFO words.  Empirical results show it to be little-endian.
>                 */
>              /* TODO: FIFO overflow checking.  */
> -            while (n--) {
> +            while (n-- && s->txp->buffer_size--) {

can you just get n right in the first place (line 766):

n = MIN(4, s->txp_buffer_size);

rather than doing min calculation on two parallel iteration variables?

Regards,
Peter

>                  s->txp->data[s->txp->len] = val & 0xff;
>                  s->txp->len++;
>                  val >>= 8;
> -                s->txp->buffer_size--;
>              }
>              s->txp->fifo_used++;
>          }
> --
> 1.7.10.4
>
>