lkml.org 
[lkml]   [2022]   [Feb]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH net-next v2 1/1] net: dsa: microchip: ksz9477: implement MTU configuration
On Thu, Feb 24, 2022 at 10:38:27AM +0100, Oleksij Rempel wrote:
> > > > > + /* Now we can configure default MTU value */
> > > > > + ret = regmap_update_bits(dev->regmap[1], REG_SW_MTU__2, REG_SW_MTU_MASK,
> > > > > + VLAN_ETH_FRAME_LEN + ETH_FCS_LEN);
> > > >
> > > > Why do you need this? Doesn't DSA call dsa_slave_create() ->
> > > > dsa_slave_change_mtu(ETH_DATA_LEN) on probe?
> > >
> > > This was my initial assumption as well, but cadence macb driver provides
> > > buggy max MTU == -18. I hardcoded bigger MTU for now[1], but was not able to
> > > find proper way to fix it. To avoid this kinds of regressions I decided
> > > to keep some sane default configuration.
> > >
> > > [1] - my workaround.
> > > commit 5f8385e9641a383478a65f96ccee8fd992201f68
> > > Author: Oleksij Rempel <linux@rempel-privat.de>
> > > Date: Mon Feb 14 14:41:06 2022 +0100
> > >
> > > WIP: net: macb: fix max mtu size
> > >
> > > The gem_readl(bp, JML) will return 0, so we get max_mtu size of -18,
> > > this is breaking MTU configuration for DSA
> > >
> > > Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> > >
> > > diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> > > index a363da928e8b..454d811991bb 100644
> > > --- a/drivers/net/ethernet/cadence/macb_main.c
> > > +++ b/drivers/net/ethernet/cadence/macb_main.c
> > > @@ -4727,7 +4727,7 @@ static int macb_probe(struct platform_device *pdev)
> > > /* MTU range: 68 - 1500 or 10240 */
> > > dev->min_mtu = GEM_MTU_MIN_SIZE;
> > > if (bp->caps & MACB_CAPS_JUMBO)
> > > - dev->max_mtu = gem_readl(bp, JML) - ETH_HLEN - ETH_FCS_LEN;
> > > + dev->max_mtu = 10240 - ETH_HLEN - ETH_FCS_LEN;
> > > else
> > > dev->max_mtu = ETH_DATA_LEN;
> >
> > Yes, but the macb driver can be a DSA master for any switch, not just
> > for ksz9477. Better to fix this differently.
>
> Yes, it should be fixed. I just need some time to understand the proper
> way to do so. For now, let's proceed with the ksz patch. Should I send
> new version with some changes?

So where is it failing exactly? Here I guess, because mtu_limit will be
negative?

mtu_limit = min_t(int, master->max_mtu, dev->max_mtu);
old_master_mtu = master->mtu;
new_master_mtu = largest_mtu + dsa_tag_protocol_overhead(cpu_dp->tag_ops);
if (new_master_mtu > mtu_limit)
return -ERANGE;

I don't think we can work around it in DSA, it's garbage in, garbage out.

In principle, I don't have such a big issue with writing the MTU
register as part of the switch initialization, especially if it's global
and not per port. But tell me something else. You pre-program the MTU
with VLAN_ETH_FRAME_LEN + ETH_FCS_LEN, but in the MTU change procedure,
you also add KSZ9477_INGRESS_TAG_LEN (2) to that. Is that needed at all?
I expect that if it's needed, it's needed in both places. Can you
sustain an iperf3 tcp session over a VLAN upper of a ksz9477 port?
I suspect that the missing VLAN_HLEN is masking a lack of KSZ9477_INGRESS_TAG_LEN.

\
 
 \ /
  Last update: 2022-02-24 10:50    [W:0.074 / U:0.372 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site