netdev - Re: [PATCH net-next v2] net: dsa: realtek: rtl8365mb: add change

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Date:   Thu, 09 Feb 2023 08:40:32 -0800
From:   Alexander H Duyck <alexander.duyck@...il.com>
To:     Luiz Angelo Daros de Luca <luizluca@...il.com>,
        netdev@...r.kernel.org
Cc:     linus.walleij@...aro.org, alsi@...g-olufsen.dk, andrew@...n.ch,
        vivien.didelot@...il.com, f.fainelli@...il.com, olteanv@...il.com,
        davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        robh+dt@...nel.org, krzk+dt@...nel.org, arinc.unal@...nc9.com
Subject: Re: [PATCH net-next v2] net: dsa: realtek: rtl8365mb: add change_mtu

On Tue, 2023-02-07 at 14:15 -0300, Luiz Angelo Daros de Luca wrote:
> rtl8365mb was using a fixed MTU size of 1536, probably inspired by
> rtl8366rb initial packet size. Different from that family, rtl8365mb
> family can specify the max packet size in bytes and not in fixed steps.
> Now it defaults to VLAN_ETH_HLEN+ETH_DATA_LEN+ETH_FCS_LEN (1522 bytes).
> 
> DSA calls change_mtu for the CPU port once the max mtu value among the
> ports changes. As the max packet size is defined globally, the switch
> is configured only when the call affects the CPU port.
> 
> The available specs do not directly define the max supported packet
> size, but it mentions a 16k limit. However, the switch sets the max
> packet size to 16368 bytes (0x3FF0) after it resets. That value was
> assumed as the maximum supported packet size.
> 
> MTU was tested up to 2018 (with 802.1Q) as that is as far as mt7620
> (where rtl8367s is stacked) can go.
> 
> There is a jumbo register, enabled by default at 6k packet size.
> However, the jumbo settings does not seem to limit nor expand the
> maximum tested MTU (2018), even when jumbo is disabled. More tests are
> needed with a device that can handle larger frames.
> 
> Signed-off-by: Luiz Angelo Daros de Luca <luizluca@...il.com>
> ---
> 
> v1->v2:
> - dropped jumbo code as it was not changing the behavior (up to 2k MTU)
> - fixed typos
> - fixed code alignment
> - renamed rtl8365mb_(change|max)_mtu to rtl8365mb_port_(change|max)_mtu
> 
>  drivers/net/dsa/realtek/rtl8365mb.c | 43 ++++++++++++++++++++++++++---
>  1 file changed, 39 insertions(+), 4 deletions(-)
> 

Looks good to me.

Reviewed-by: Alexander Duyck <alexanderduyck@...com>