netdev - Re: [PATCH net-next v25 06/13] rtase: Implement .ndo_start

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Message-ID: <20240729191424.589aff98@kernel.org>
Date: Mon, 29 Jul 2024 19:14:24 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Justin Lai <justinlai0215@...ltek.com>
Cc: <davem@...emloft.net>, <edumazet@...gle.com>, <pabeni@...hat.com>,
 <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>, <andrew@...n.ch>,
 <jiri@...nulli.us>, <horms@...nel.org>, <rkannoth@...vell.com>,
 <jdamato@...tly.com>, <pkshih@...ltek.com>, <larry.chiu@...ltek.com>
Subject: Re: [PATCH net-next v25 06/13] rtase: Implement .ndo_start_xmit
 function

On Mon, 29 Jul 2024 14:21:14 +0800 Justin Lai wrote:
> +	stop_queue = !netif_subqueue_maybe_stop(dev, ring->index,
> +						rtase_tx_avail(ring),
> +						RTASE_TX_STOP_THRS,
> +						RTASE_TX_START_THRS);
> +
> +	if (door_bell || stop_queue)
> +		rtase_w8(tp, RTASE_TPPOLL, BIT(ring->index));
> +
> +	return NETDEV_TX_OK;
> +
> +err_dma_1:
> +	ring->skbuff[entry] = NULL;
> +	rtase_tx_clear_range(ring, ring->cur_idx + 1, frags);
> +
> +err_dma_0:
> +	tp->stats.tx_dropped++;
> +	dev_kfree_skb_any(skb);
> +	return NETDEV_TX_OK;
> +
> +err_stop:
> +	netif_stop_queue(dev);
> +	tp->stats.tx_dropped++;
> +	return NETDEV_TX_BUSY;

If you're dropping a packet you should somehow check that the previous
xmit didn't enqueue a packet to the ring and skip the doorbell because
door_bell was false. If that's the case you have to ring the doorbell now.

Also you shouldn't increment dropped if you return TX_BUSY.

Please fix these issues in the driver you're copying from, too.