On Sun, Oct 23, 2016 at 04:30:56PM +0200, Stefan Richter wrote:
> firewire-net, like the older eth1394 driver, reduced the initial MTU to
> less than 1500 octets if the local link layer controller's asynchronous
> packet reception limit was lower.
>
> This is bogus, since this reception limit does not have anything to do
> with the transmission limit. Neither did this reduction affect the TX
> path positively, nor could it prevent link fragmentation at the RX path.
>
> Many FireWire CardBus cards have a max_rec of 9, causing an initial MTU
> of 1024 - 16 = 1008. RFC 2734 and RFC 3146 allow a minimum max_rec = 8,
> which would result in an initial MTU of 512 - 16 = 496. On such cards,
> IPv6 could only be employed if the MTU was manually increased to 1280 or
> more, i.e. IPv6 would not work without intervention from userland.
>
> We now always initialize the MTU to 1500, which is the default according
> to RFC 2734 and RFC 3146.
>
> On a VIA VT6316 based CardBus card which was affected by this, changing
> the MTU from 1008 to 1500 also increases TX bandwidth by 6 %.
> RX remains unaffected.
>
> CC: net...@vger.kernel.org
> CC: linux1394-de...@lists.sourceforge.net
> CC: Jarod Wilson
> Signed-off-by: Stefan Richter
> ---
> drivers/firewire/net.c | 8 +---
> 1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
> index 99379542b263..03715e7d9d92 100644
> --- a/drivers/firewire/net.c
> +++ b/drivers/firewire/net.c
> @@ -1463,13 +1463,7 @@ static int fwnet_probe(struct fw_unit *unit,
> goto out;
> dev->local_fifo = dev->handler.offset;
>
> - /*
> - * Use the RFC 2734 default 1500 octets or the maximum payload
> - * as initial MTU
> - */
> - net->mtu = min(1500U,
> -(1U << (card->max_receive + 1))
> -- RFC2374_FRAG_HDR_SIZE - IEEE1394_GASP_HDR_SIZE);
> + net->mtu = 1500U;
Should be able to do just net->mtu = ETH_DATA_LEN;
--
Jarod Wilson
ja...@redhat.com
