Re: [PATCH 3/3] net: ethernet: ti: am65-cpsw: Add device tree property to set max MTU

["Sanjuán García, Jorge" <Jorge.SanjuanGarcia@duagon.com>]

On Tue, 2024-01-02 at 16:03 +0530, Siddharth Vadapalli wrote:
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> 
> Hello,

Hello,

First of all thanks for the quick review. Some comments bellow:

> 
> On 02-01-2024 13:49, Sanjuán García, Jorge wrote:
> > The switch supports ethernet frame sizes between 64 and 2024 bytes
> > (including VLAN) as stated in the technical reference manual.
> 
> Could you please share the source for the "2024 bytes" mentioned
> above?
> In J7200 SoC's TRM, I see support for up to 9604 bytes (including
> VLAN)
> in the "CPSW_PN_RX_MAXLEN_REG_k" register description for CPSW5G
> instance of CPSW.
> 

The 2024 bytes as max value I got it from the AM6442 TRF which is the
SoC I have been working on. At least for port 0, the register
CPSW_P0_RX_MAXLEN_REG is documented as: "The maximum value is
9604 (including VLAN) when fifo_blk_size = 4. When fifo_blk_size = 1
the maximum value is 2024 (including VLAN)". It is not clear to me how
the fifo_blk_size should work from the reference manual so I kept it
safe to those 2024 bytes. Please let me know if something else should
be considered.

> > 
> > This patch adds a new devicetree property so the switch ports can
> > be configured with an MTU higher than the standar 1500 bytes,
> > making
> 
> nitpick: standar/standard.

Oops.

> 
> > the max frame length configured on the registers and the max_mtu
> > advertised on the network device consistent.
> > 
> > Signed-off-by: Jorge Sanjuan Garcia
> > <jorge.sanjuangarcia@duagon.com>
> > ---
> 
> For patches which add new features, please use the subject prefix
> [PATCH net-next].
> 
> >   drivers/net/ethernet/ti/am65-cpsw-nuss.c | 18 ++++++++++++++----
> >   drivers/net/ethernet/ti/am65-cpsw-nuss.h |  1 +
> >   2 files changed, 15 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > index a920146d7a60..6a5c8b6e03f4 100644
> > --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> > @@ -56,7 +56,7 @@
> >   #define AM65_CPSW_MAX_PORTS     8
> > 
> >   #define AM65_CPSW_MIN_PACKET_SIZE       VLAN_ETH_ZLEN
> > -#define AM65_CPSW_MAX_PACKET_SIZE      (VLAN_ETH_FRAME_LEN +
> > ETH_FCS_LEN)
> > +#define AM65_CPSW_MAX_PACKET_SIZE      2024
> > 
> >   #define AM65_CPSW_REG_CTL               0x004
> >   #define AM65_CPSW_REG_STAT_PORT_EN      0x014
> > @@ -2198,8 +2198,7 @@ am65_cpsw_nuss_init_port_ndev(struct
> > am65_cpsw_common
> > *common, u32 port_idx)
> >           eth_hw_addr_set(port->ndev, port->slave.mac_addr);
> > 
> >           port->ndev->min_mtu = AM65_CPSW_MIN_PACKET_SIZE;
> > -       port->ndev->max_mtu = common->rx_packet_max -
> > -                             (VLAN_ETH_HLEN + ETH_FCS_LEN);
> > +       port->ndev->max_mtu = common->max_mtu;
> 
> This seems to be modifying what was added in just the previous patch.
> Isn't it better to merge these changes into a single patch?

Yeah. I was not sure about whether it would be best to split the new
struct member and the device tree parsing into two patches. I'll merge
patches 2/3 and 3/3 of this series as one patch with the updates.

> 
> >           port->ndev->hw_features = NETIF_F_SG |
> >                                     NETIF_F_RXCSUM |
> >                                     NETIF_F_HW_CSUM |
> > @@ -2927,8 +2926,19 @@ static int am65_cpsw_nuss_probe(struct
> > platform_device *pdev)
> >           if (common->port_num < 1 || common->port_num >
> > AM65_CPSW_MAX_PORTS)
> >                   return -ENOENT;
> > 
> > +       common->max_mtu = VLAN_ETH_DATA_LEN;
> > +       of_property_read_u32(dev->of_node, "max-frame-size",
> > &common->max_mtu);
> 
> The device-tree property "max-frame-size" is a port-specific
> property.
> Therefore, it is wrong to expect the property to be present at the
> CPSW
> node level instead of being present within each port in the
> "ethernet-ports" node. This section should be moved into the
> function:
> am65_cpsw_nuss_init_slave_ports()
> which parses the device-tree nodes for each port. The "max-frame-
> size"
> property can be stored there on a per-port basis within a newly added
> member in "struct am65_cpsw_port" as mentioned in my previous mail
> for
> patch 2/3.
> 

That makes sense. I agree this should be a per slave port property.
I'll start putting together a version 2 doing it that way. I need to
think about what we should do with port 0's max frame size.

> > +
> > +       common->rx_packet_max = common->max_mtu + VLAN_ETH_HLEN +
> > ETH_FCS_LEN;
> > +       if (common->rx_packet_max > AM65_CPSW_MAX_PACKET_SIZE) {
> > +               common->rx_packet_max = AM65_CPSW_MAX_PACKET_SIZE;
> > +               common->max_mtu = AM65_CPSW_MAX_PACKET_SIZE -
> > +                                 (VLAN_ETH_HLEN + ETH_FCS_LEN);
> > +       }
> > +
> > +       dev_info(common->dev, "Max RX packet size set to %d\n",
> > common->rx_packet_max);
> > +
> >           common->rx_flow_id_base = -1;
> > -       common->rx_packet_max = AM65_CPSW_MAX_PACKET_SIZE;
> >           init_completion(&common->tdown_complete);
> >           common->tx_ch_num = AM65_CPSW_DEFAULT_TX_CHNS;
> >           common->pf_p0_rx_ptype_rrobin = false;
> > diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.h
> > b/drivers/net/ethernet/ti/am65-cpsw-nuss.h
> > index 141160223d73..3bb0ff94a46a 100644
> > --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.h
> > +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.h
> > @@ -130,6 +130,7 @@ struct am65_cpsw_common {
> >           u32                     tx_ch_rate_msk;
> >           u32                     rx_flow_id_base;
> > 
> > +       int                     max_mtu;
> >           int                     rx_packet_max;
> > 
> >           struct am65_cpsw_tx_chn tx_chns[AM65_CPSW_MAX_TX_QUEUES];
> 
> ...
> 
> --
> Regards,
> Siddharth.

Regards,
Jorge