linux-kernel - Re: [PATCH v12 06/10] net: ti: icssg-prueth: Add ICSSG ethernet driver

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Date:   Fri, 28 Jul 2023 17:24:19 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     MD Danish Anwar <danishanwar@...com>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Roger Quadros <rogerq@...nel.org>,
        Simon Horman <simon.horman@...igine.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Andrew Lunn <andrew@...n.ch>,
        Richard Cochran <richardcochran@...il.com>,
        Conor Dooley <conor+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>, <nm@...com>, <srk@...com>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v12 06/10] net: ti: icssg-prueth: Add ICSSG ethernet
 driver

On Thu, 27 Jul 2023 16:58:23 +0530 MD Danish Anwar wrote:
> +static int emac_tx_complete_packets(struct prueth_emac *emac, int chn,
> +				    int budget)
> +{
> +	struct net_device *ndev = emac->ndev;
> +	struct cppi5_host_desc_t *desc_tx;
> +	struct netdev_queue *netif_txq;
> +	struct prueth_tx_chn *tx_chn;
> +	unsigned int total_bytes = 0;
> +	struct sk_buff *skb;
> +	dma_addr_t desc_dma;
> +	int res, num_tx = 0;
> +	void **swdata;
> +
> +	tx_chn = &emac->tx_chns[chn];
> +
> +	while (budget) {
> +		res = k3_udma_glue_pop_tx_chn(tx_chn->tx_chn, &desc_dma);
> +		if (res == -ENODATA)
> +			break;

You shouldn't limit the number of serviced packets to budget for Tx
NAPI.

https://docs.kernel.org/next/networking/napi.html#driver-api

> +	skb->dev = ndev;
> +	if (!netif_running(skb->dev)) {
> +		dev_kfree_skb_any(skb);
> +		return 0;
> +	}

why do you check if the interface is running?
If a packet arrives, it means the interface is running..

> +drop_free_descs:
> +	prueth_xmit_free(tx_chn, first_desc);
> +drop_stop_q:
> +	netif_tx_stop_queue(netif_txq);

Do not stop the queue on DMA errors. If the queue is empty nothing
will wake it up. Queue should only be stopped based on occupancy.

> +	dev_kfree_skb_any(skb);
> +
> +	/* error */
> +	ndev->stats.tx_dropped++;
> +	netdev_err(ndev, "tx: error: %d\n", ret);
> +
> +	return ret;
-- 
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