Re: [PATCH net-next 09/11] net: dsa: rzn1-a5psw: Add support for management port frame length adjustment

Vladimir Oltean
2025-11-21T21:05:10Z

On Fri, Nov 21, 2025 at 11:35:35AM +0000, Prabhakar wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
>
> Extend the RZN1 A5PSW driver to support SoC-specific adjustments to the
> management (CPU) port frame length. Some SoCs, such as the RZ/T2H and
> RZ/N2H, require additional headroom on the management port to account
> for a special management tag added to frames. Without this adjustment,
> frames may be incorrectly detected as oversized and subsequently
> discarded.
>
> Introduce a new field, `management_port_frame_len_adj`, in
> `struct a5psw_of_data` to represent this adjustment, and apply it in
> `a5psw_port_change_mtu()` when configuring the frame length for the
> CPU port.
>
> This change prepares the driver for use on RZ/T2H and RZ/N2H SoCs.

In the next change you set this to 40. What's the reason behind such a
high value (need to set the management port A5PSW_FRM_LENGTH value to
1574 bytes to pass L2 payload of 1500 bytes)? It sounds like this needs
to be called out more clearly for what it is - a hardware bug.