netdev - Re: [PATCH net v2] net: lantiq_xrx200: increase buffer reservation

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Date:   Tue, 7 Dec 2021 20:54:48 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Aleksander Jan Bajkowski <olek2@...pl>
Cc:     hauke@...ke-m.de, davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net: lantiq_xrx200: increase buffer reservation

On Mon,  6 Dec 2021 23:39:09 +0100 Aleksander Jan Bajkowski wrote:
> +static int xrx200_max_frame_len(int mtu)
> +{
> +	return VLAN_ETH_HLEN + mtu + ETH_FCS_LEN;

You sure the problem is not that this doesn't include ETH_HLEN? 
MTU is the length of the L2 _payload_.

> +}
> +
> +static int xrx200_buffer_size(int mtu)
> +{
> +	return round_up(xrx200_max_frame_len(mtu) - 1, 4 * XRX200_DMA_BURST_LEN);

Why the - 1 ? 🤔

For a frame size 101 => max_frame_len 109 you'll presumably want 
the buffer to be 116, not 108?

> +}
> +