Re: [PATCH net-next v4 4/4] net: dsa: microchip: ksz8: add MTU configuration support

On Thu, Nov 10, 2022 at 01:22:25PM +0100, Oleksij Rempel wrote:

Make MTU configurable on KSZ87xx and KSZ88xx series of switches.

Before this patch, pre-configured behavior was different on different
switch series, due to opposite meaning of the same bit:
- KSZ87xx: Reg 4, Bit 1 - if 1, max frame size is 1532; if 0 - 1514
- KSZ88xx: Reg 4, Bit 1 - if 1, max frame size is 1514; if 0 - 1532

Since the code was telling "... SW_LEGAL_PACKET_DISABLE, true)", I
assume, the idea was to set max frame size to 1532.

With this patch, by setting MTU size 1500, both switch series will be
configured to the 1532 frame limit.

This patch was tested on KSZ8873.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
---

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>

As an extension to this patch set, you might also want to set
ds->mtu_enforcement_ingress = true, to activate the bridge MTU
normalization logic, since you have one MTU global to the entire switch.