Messages in this thread | | | Date | Thu, 24 Feb 2022 10:38:27 +0100 | From | Oleksij Rempel <> | Subject | Re: [PATCH net-next v2 1/1] net: dsa: microchip: ksz9477: implement MTU configuration |
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On Thu, Feb 24, 2022 at 11:33:29AM +0200, Vladimir Oltean wrote: > On Thu, Feb 24, 2022 at 05:59:36AM +0100, Oleksij Rempel wrote: > > > Are you sure the unit of measurement is ok? My KSZ9477 documentation > > > says this about register 0x0308: > > > > > > Maximum Frame Length (MTU) > > > Specifies the maximum transmission unit (MTU), which is the maximum > > > frame payload size. Frames which exceed this maximum are truncated. This > > > value can be set as high as 9000 (= 0x2328) if jumbo frame support is > > > required. > > > > > > "frame payload" to me means what MTU should mean. And ETH_HLEN + > > > VLAN_HLEN + ETH_FCS_LEN isn't part of that meaning. > > > > if I set this value to anything less then 1522, it breaks the NFS boot. Since > > my NFS server is configured with MTU 1500, i tried to guess how > > frame size is calculated on this chip. > > Sad that Microchip engineers can't decide on whether the MTU register > holds the "Maximum Frame Length" or the "maximum frame payload size". > They said both to have themselves covered, you understand what you will, > of course both are not right :)
¯\_(ツ)_/¯
> > > > + /* 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?
Regards, Oleksij -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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