On Sat, Jul 18, 2020 at 01:38:08PM +0300, Vladimir Oltean wrote:
> On Sat, Jul 18, 2020 at 10:35:55AM +0100, Jonathan McDowell wrote:
> > This switch has a single max frame size configuration register, so we
> > track the requested MTU for each port and apply the largest.
> > 
> > Signed-off-by: Jonathan McDowell <nood...@earth.li>
> > ---
> >  drivers/net/dsa/qca8k.c | 38 ++++++++++++++++++++++++++++++++++++++
> >  drivers/net/dsa/qca8k.h |  3 +++
> >  2 files changed, 41 insertions(+)
> > 
> > diff --git a/drivers/net/dsa/qca8k.c b/drivers/net/dsa/qca8k.c
> > index 4acad5fa0c84..3690f02aea3a 100644
> > --- a/drivers/net/dsa/qca8k.c
> > +++ b/drivers/net/dsa/qca8k.c
> > @@ -670,6 +670,12 @@ qca8k_setup(struct dsa_switch *ds)
> >             }
> >     }
> >  
> > +   /* Setup our port MTUs to match power on defaults */
> > +   for (i = 0; i < QCA8K_NUM_PORTS; i++) {
> > +           priv->port_mtu[i] = ETH_FRAME_LEN + ETH_FCS_LEN;
> > +   }
> 
> I am not quite sure the curly brackets are needed. And nowhere else in
> qca8k.c is this convention being used.

Good point; force of habit from coding standards elsewhere. Fixed (and
also the instance below).

> > +   qca8k_write(priv, QCA8K_MAX_FRAME_SIZE, ETH_FRAME_LEN + ETH_FCS_LEN);
> > +
> >     /* Flush the FDB table */
> >     qca8k_fdb_flush(priv);
> >  
> > @@ -1098,6 +1104,36 @@ qca8k_port_disable(struct dsa_switch *ds, int port)
> >     priv->port_sts[port].enabled = 0;
> >  }
> >  
> > +static int
> > +qca8k_port_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
> > +{
> > +   struct qca8k_priv *priv = ds->priv;
> > +   int i, mtu;
> > +
> > +   if ((new_mtu < ETH_MIN_MTU) || (new_mtu > QCA8K_MAX_MTU)) {
> > +           return -EINVAL;
> > +   }
> 
> I'm pretty sure this check should not be needed.
> The only reason why slave_dev->min_mtu is 0 seems to be:
> 
> commit 8b1efc0f83f1f75b8f85c70d2211007de8fd7633
> Author: Jarod Wilson <ja...@redhat.com>
> Date:   Thu Oct 20 23:25:27 2016 -0400
> 
>     net: remove MTU limits on a few ether_setup callers
> 
>     These few drivers call ether_setup(), but have no ndo_change_mtu, and thus
>     were overlooked for changes to MTU range checking behavior. They
>     previously had no range checks, so for feature-parity, set their min_mtu
>     to 0 and max_mtu to ETH_MAX_MTU (65535), instead of the 68 and 1500
>     inherited from the ether_setup() changes. Fine-tuning can come after we 
> get
>     back to full feature-parity here.
> 
>     CC: netdev@vger.kernel.org
>     Reported-by: Asbjoern Sloth Toennesen <asbj...@asbjorn.st>
>     CC: Asbjoern Sloth Toennesen <asbj...@asbjorn.st>
>     CC: R Parameswaran <parameswaran...@gmail.com>
>     Signed-off-by: Jarod Wilson <ja...@redhat.com>
>     Signed-off-by: David S. Miller <da...@davemloft.net>
> 
> which is an oversight on my part. Since now DSA supports
> ndo_change_mtu(), the "slave_dev->min_mtu = 0;" line in net/dsa/slave.c
> can be removed and so can this check.

Ok.

> > +
> > +   priv->port_mtu[port] = new_mtu;
> > +
> > +   mtu = 0;
> 
> I think it's more typical to initialize mtu to 0 at declaration time.

Sure, fixed.

> > +   for (i = 0; i < QCA8K_NUM_PORTS; i++) {
> > +           if (priv->port_mtu[port] > mtu)
> > +                   mtu = priv->port_mtu[port];
> > +   }
> 
> Again, curly brackets are not needed here, although some might feel it
> aids readability.
> 
> > +
> > +   /* Include L2 header / FCS length */
> > +   qca8k_write(priv, QCA8K_MAX_FRAME_SIZE, mtu + ETH_HLEN + ETH_FCS_LEN);
> > +
> > +   return 0;
> > +}
> > +
> > +static int
> > +qca8k_port_max_mtu(struct dsa_switch *ds, int port)
> > +{
> > +   return QCA8K_MAX_MTU;
> 
> So what is the maximum value that you can write into
> QCA8K_MAX_FRAME_SIZE? 9000 or 9018? If it's 9000, you should report a
> max MTU of 8982, and let the network stack do the range check for you,
> that's why this callback exists in the first place.

9018 (including header + fcs), hence returning QCA8K_MAX_MTU here.

> Do you know how are VLAN tags accounted for (i.e. does iperf3 TCP work
> over a VLAN sub-interface after your patch)? There are 2 options:
> - The ports automatically increase the maximum accepted frame size by 4
>   (or 8, in case of double tag) bytes if they see VLAN tagged traffic.
>   Case in which you don't need to do anything.
> - You need to manually account for the possibility that VLAN-tagged
>   traffic will be received, since the 802.1Q header is not part of the
>   SDU whose max length is measured by the MTU. So you might want to
>   write a value to QCA8K_MAX_FRAME_SIZE that is either "mtu +
>   VLAN_ETH_HLEN + ETH_FCS_LEN", or "mtu + ETH_HLEN + 2 * VLAN_HLEN +
>   ETH_FCS_LEN", depending on whether you foresee double-tagging being
>   used.

The value is for a normal packet; the switch accounts for VLAN / double
VLAN / the switch tagging header size itself.

> > +}
> > +
> >  static int
> >  qca8k_port_fdb_insert(struct qca8k_priv *priv, const u8 *addr,
> >                   u16 port_mask, u16 vid)
> > @@ -1174,6 +1210,8 @@ static const struct dsa_switch_ops qca8k_switch_ops = 
> > {
> >     .set_mac_eee            = qca8k_set_mac_eee,
> >     .port_enable            = qca8k_port_enable,
> >     .port_disable           = qca8k_port_disable,
> > +   .port_change_mtu        = qca8k_port_change_mtu,
> > +   .port_max_mtu           = qca8k_port_max_mtu,
> >     .port_stp_state_set     = qca8k_port_stp_state_set,
> >     .port_bridge_join       = qca8k_port_bridge_join,
> >     .port_bridge_leave      = qca8k_port_bridge_leave,
> > diff --git a/drivers/net/dsa/qca8k.h b/drivers/net/dsa/qca8k.h
> > index 10ef2bca2cde..31439396401c 100644
> > --- a/drivers/net/dsa/qca8k.h
> > +++ b/drivers/net/dsa/qca8k.h
> > @@ -13,6 +13,7 @@
> >  #include <linux/gpio.h>
> >  
> >  #define QCA8K_NUM_PORTS                                    7
> > +#define QCA8K_MAX_MTU                                      9000
> >  
> >  #define PHY_ID_QCA8337                                     0x004dd036
> >  #define QCA8K_ID_QCA8337                           0x13
> > @@ -58,6 +59,7 @@
> >  #define   QCA8K_MDIO_MASTER_MAX_REG                        32
> >  #define QCA8K_GOL_MAC_ADDR0                                0x60
> >  #define QCA8K_GOL_MAC_ADDR1                                0x64
> > +#define QCA8K_MAX_FRAME_SIZE                               0x78
> >  #define QCA8K_REG_PORT_STATUS(_i)                  (0x07c + (_i) * 4)
> >  #define   QCA8K_PORT_STATUS_SPEED                  GENMASK(1, 0)
> >  #define   QCA8K_PORT_STATUS_SPEED_10                       0
> > @@ -189,6 +191,7 @@ struct qca8k_priv {
> >     struct device *dev;
> >     struct dsa_switch_ops ops;
> >     struct gpio_desc *reset_gpio;
> > +   unsigned int port_mtu[QCA8K_NUM_PORTS];
> >  };
> >  
> >  struct qca8k_mib_desc {
> > -- 
> > 2.27.0

J.

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