When tx_max_frame_size was added to struct ravb_hw_info, no value was
set in ravb_rzv2m_hw_info so the default value of zero was used.

The maximum MTU is set by subtracting from tx_max_frame_size to allow
space for headers and frame checksums. As ndev->max_mtu is unsigned,
this subtraction wraps around leading to a ridiculously large positive
value that is obviously incorrect.

Before tx_max_frame_size was introduced, the maximum MTU was based on
rx_max_frame_size. So, we can restore the correct maximum MTU by copying
the rx_max_frame_size value into tx_max_frame_size for RZ/V2M.

Fixes: 1d63864299ca ("net: ravb: Fix maximum TX frame size for GbEth devices")
Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
---
 drivers/net/ethernet/renesas/ravb_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index ac0f093f647a..bc395294a32d 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2763,6 +2763,7 @@ static const struct ravb_hw_info ravb_rzv2m_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,
 	.rx_max_frame_size = SZ_2K,
 	.rx_buffer_size = SZ_2K +
 			  SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),

base-commit: 2d2d4f60ed266a8f340a721102d035252606980b
-- 
2.39.5

On 1/9/25 2:37 PM, Paul Barker wrote:

> When tx_max_frame_size was added to struct ravb_hw_info, no value was
> set in ravb_rzv2m_hw_info so the default value of zero was used.
> 
> The maximum MTU is set by subtracting from tx_max_frame_size to allow
> space for headers and frame checksums. As ndev->max_mtu is unsigned,
> this subtraction wraps around leading to a ridiculously large positive
> value that is obviously incorrect.
> 
> Before tx_max_frame_size was introduced, the maximum MTU was based on
> rx_max_frame_size. So, we can restore the correct maximum MTU by copying
> the rx_max_frame_size value into tx_max_frame_size for RZ/V2M.

   Seems to be reviewers' fault as well?

> Fixes: 1d63864299ca ("net: ravb: Fix maximum TX frame size for GbEth devices")
> Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>

Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>

MBR, Sergey

On Thu, Jan 09, 2025 at 11:37:06AM +0000, Paul Barker wrote:
> When tx_max_frame_size was added to struct ravb_hw_info, no value was
> set in ravb_rzv2m_hw_info so the default value of zero was used.
> 
> The maximum MTU is set by subtracting from tx_max_frame_size to allow
> space for headers and frame checksums. As ndev->max_mtu is unsigned,
> this subtraction wraps around leading to a ridiculously large positive
> value that is obviously incorrect.
> 
> Before tx_max_frame_size was introduced, the maximum MTU was based on
> rx_max_frame_size. So, we can restore the correct maximum MTU by copying
> the rx_max_frame_size value into tx_max_frame_size for RZ/V2M.
> 
> Fixes: 1d63864299ca ("net: ravb: Fix maximum TX frame size for GbEth devices")
> Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>

Reviewed-by: Simon Horman <horms@kernel.org>

...

Hi Paul,

Nice catch.

On 2025-01-09 11:37:06 +0000, Paul Barker wrote:
> When tx_max_frame_size was added to struct ravb_hw_info, no value was
> set in ravb_rzv2m_hw_info so the default value of zero was used.
> 
> The maximum MTU is set by subtracting from tx_max_frame_size to allow
> space for headers and frame checksums. As ndev->max_mtu is unsigned,
> this subtraction wraps around leading to a ridiculously large positive
> value that is obviously incorrect.
> 
> Before tx_max_frame_size was introduced, the maximum MTU was based on
> rx_max_frame_size. So, we can restore the correct maximum MTU by copying
> the rx_max_frame_size value into tx_max_frame_size for RZ/V2M.
> 
> Fixes: 1d63864299ca ("net: ravb: Fix maximum TX frame size for GbEth devices")
> Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>

Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>

> ---
>  drivers/net/ethernet/renesas/ravb_main.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index ac0f093f647a..bc395294a32d 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -2763,6 +2763,7 @@ static const struct ravb_hw_info ravb_rzv2m_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,
>  	.rx_max_frame_size = SZ_2K,
>  	.rx_buffer_size = SZ_2K +
>  			  SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
> 
> base-commit: 2d2d4f60ed266a8f340a721102d035252606980b
> -- 
> 2.39.5
> 

-- 
Kind Regards,
Niklas Söderlund