Messages in this thread Patch in this message | | | Date | Thu, 24 Feb 2022 05:59:36 +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 01:38:33AM +0200, Vladimir Oltean wrote: > On Wed, Feb 23, 2022 at 09:40:55AM +0100, Oleksij Rempel wrote: > > This chips supports two ways to configure max MTU size: > > - by setting SW_LEGAL_PACKET_DISABLE bit: if this bit is 0 allowed packed size > > will be between 64 and bytes 1518. If this bit is 1, it will accept > > packets up to 2000 bytes. > > - by setting SW_JUMBO_PACKET bit. If this bit is set, the chip will > > ignore SW_LEGAL_PACKET_DISABLE value and use REG_SW_MTU__2 register to > > configure MTU size. > > > > Current driver has disabled SW_JUMBO_PACKET bit and activates > > SW_LEGAL_PACKET_DISABLE. So the switch will pass all packets up to 2000 without > > any way to configure it. > > > > By providing port_change_mtu we are switch to SW_JUMBO_PACKET way and will > > be able to configure MTU up to ~9000. > > > > Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de> > > --- > > changes v2: > > - rename max_mtu to max_frame and new_mtu to frame_size > > - use max() instead of if(>) > > --- > > drivers/net/dsa/microchip/ksz9477.c | 40 +++++++++++++++++++++++-- > > drivers/net/dsa/microchip/ksz9477_reg.h | 4 +++ > > drivers/net/dsa/microchip/ksz_common.h | 1 + > > 3 files changed, 43 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c > > index 18ffc8ded7ee..5c5f78cb970e 100644 > > --- a/drivers/net/dsa/microchip/ksz9477.c > > +++ b/drivers/net/dsa/microchip/ksz9477.c > > @@ -11,6 +11,7 @@ > > #include <linux/platform_data/microchip-ksz.h> > > #include <linux/phy.h> > > #include <linux/if_bridge.h> > > +#include <linux/if_vlan.h> > > #include <net/dsa.h> > > #include <net/switchdev.h> > > > > @@ -182,6 +183,33 @@ static void ksz9477_port_cfg32(struct ksz_device *dev, int port, int offset, > > bits, set ? bits : 0); > > } > > > > +static int ksz9477_change_mtu(struct dsa_switch *ds, int port, int mtu) > > +{ > > + struct ksz_device *dev = ds->priv; > > + u16 frame_size, max_frame = 0; > > + int i; > > + > > + frame_size = mtu + ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN; > > 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.
> > + > > + if (dsa_is_cpu_port(ds, port)) > > + frame_size += KSZ9477_INGRESS_TAG_LEN; > > + > > + /* Cache the per-port MTU setting */ > > + dev->ports[port].max_frame = frame_size; > > + > > + for (i = 0; i < dev->port_cnt; i++) > > + max_frame = max(max_frame, dev->ports[i].max_frame); > > + > > + return regmap_update_bits(dev->regmap[1], REG_SW_MTU__2, > > + REG_SW_MTU_MASK, max_frame); > > +} > > + > > +static int ksz9477_max_mtu(struct dsa_switch *ds, int port) > > +{ > > + return KSZ9477_MAX_FRAME_SIZE - ETH_HLEN - ETH_FCS_LEN - VLAN_HLEN - > > + KSZ9477_INGRESS_TAG_LEN; > > +} > > + > > static int ksz9477_wait_vlan_ctrl_ready(struct ksz_device *dev) > > { > > unsigned int val; > > @@ -1412,8 +1440,14 @@ static int ksz9477_setup(struct dsa_switch *ds) > > /* Do not work correctly with tail tagging. */ > > ksz_cfg(dev, REG_SW_MAC_CTRL_0, SW_CHECK_LENGTH, false); > > > > - /* accept packet up to 2000bytes */ > > - ksz_cfg(dev, REG_SW_MAC_CTRL_1, SW_LEGAL_PACKET_DISABLE, true); > > + /* Enable REG_SW_MTU__2 reg by setting SW_JUMBO_PACKET */ > > + ksz_cfg(dev, REG_SW_MAC_CTRL_1, SW_JUMBO_PACKET, true); > > + > > + /* 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; -- 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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