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Date:   Sat, 4 Nov 2023 15:56:59 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     Linus Walleij <linus.walleij@linaro.org>
Cc:     Hans Ulli Kroll <ulli.kroll@googlemail.com>,
        "David S. Miller" <davem@davemloft.net>,
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        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net 4/4] net: ethernet: cortina: Handle large frames
Message-ID: <036b481e-ac5b-4e77-b93a-4badaf19e185@lunn.ch>
References: <20231104-gemini-largeframe-fix-v1-0-9c5513f22f33@linaro.org>
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> @@ -1170,7 +1171,14 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
>  		word3 |= mtu;
>  	}
>  
> -	if (skb->ip_summed != CHECKSUM_NONE) {
> +	if (skb->len >= ETH_FRAME_LEN) {
> +		/* Hardware offloaded checksumming isn't working on frames
> +		 * bigger than 1514 bytes. Perhaps the buffer is only 1518
> +		 * bytes fitting mach a normal frame and a checksum?

mach ?

> +		 * Just bypass on bigger frames.
> +		 */
> +		word1 |= TSS_BYPASS_BIT;
> +	} else if (skb->ip_summed != CHECKSUM_NONE) {

I've never looked at how the network stack does checksums. But looking
at this patch, it made me wounder, how do you tell the stack it needs
to do a software checksum because the hardware cannot? Or for this
driver, is it always calculating a checksum, which is then ignored?
Maybe you can improve performance a little but disabling software
checksum when it is not needed?

	 Andrew