linux-kernel - Re: [net-next PATCH 1/2] net: ravb: Fix maximum MTU for GbEth devices

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Message-ID: <ce098866-4619-4570-9a82-5b2399d52d31@bp.renesas.com>
Date: Tue, 13 Aug 2024 14:37:13 +0100
From: Paul Barker <paul.barker.ct@...renesas.com>
To: Sergey Shtylyov <s.shtylyov@....ru>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
Cc: Biju Das <biju.das.jz@...renesas.com>,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
 Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
 Mitsuhiro Kimura <mitsuhiro.kimura.kc@...esas.com>, netdev@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [net-next PATCH 1/2] net: ravb: Fix maximum MTU for GbEth devices

On 17/06/2024 20:38, Sergey Shtylyov wrote:
> On 6/15/24 1:30 PM, Paul Barker wrote:
> 
>> The datasheets for all SoCs using the GbEth IP specify a maximum
>> transmission frame size of 1.5 kByte. I've confirmed through internal
>> discussions that support for 1522 byte frames has been validated, which
>> allows us to support the default MTU of 1500 bytes after reserving space
>> for the Ethernet header, frame checksums and an optional VLAN tag.
>>
>> Fixes: 2e95e08ac009 ("ravb: Add rx_max_buf_size to struct ravb_hw_info")
>> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>
> [...]
> 
> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>
> 
>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>> index c1546b916e4e..02cbf850bd85 100644
>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>> @@ -2664,6 +2664,7 @@ static const struct ravb_hw_info ravb_gen3_hw_info = {
>>  	.net_features = NETIF_F_RXCSUM,
>>  	.stats_len = ARRAY_SIZE(ravb_gstrings_stats),
>>  	.tccr_mask = TCCR_TSRQ0 | TCCR_TSRQ1 | TCCR_TSRQ2 | TCCR_TSRQ3,
>> +	.tx_max_frame_size = SZ_2K,
> 
>    The R-Car gen3 manual says 2047... Typo? :-)

Apologies for the late response.

The maximum MTU is currently based on rx_max_frame_size which is SZ_2K
for the R-Car gen3 devices. So this should be addressed in two commits:

* This commit to address the GbEth MTU, leaving the R-Car gen3 MTU
  incorrect.

* A second commit to address the R-Car gen3 MTU.

Unfortunately I have no test environment where I can properly
investigate jumbo packet behaviour with a R-Car gen3 boards so I
recommend the second commit is sent by someone who can test it fully.

Thanks,

-- 
Paul Barker