netdev - Re: [PATCH net-next 2/3] net: ethernet: socionext: add AVE ethernet driver

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Date:   Mon, 11 Sep 2017 15:56:32 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH net-next 2/3] net: ethernet: socionext: add AVE ethernet driver

Hi Florian,

On Sat, 9 Sep 2017 09:30:58 -0700 <f.fainelli@...il.com> wrote:

> 
> 
> On 09/08/2017 06:02 AM, Kunihiko Hayashi wrote:
> > The UniPhier platform from Socionext provides the AVE ethernet
> > controller that includes MAC and MDIO bus supporting RGMII/RMII
> > modes. The controller is named AVE.
> > 
> > Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
> > Signed-off-by: Jassi Brar <jaswinder.singh@...aro.org>
> > ---
> 
> [snip]
> 
> > +static int ave_start_xmit(struct sk_buff *skb, struct net_device *ndev)
> > +{
> > +	struct ave_private *priv = netdev_priv(ndev);
> > +	u32 proc_idx, done_idx, ndesc, cmdsts;
> > +	int freepkt;
> > +	unsigned char *buffptr = NULL; /* buffptr for descriptor */
> > +	unsigned int len;
> > +	dma_addr_t paddr;
> > +
> > +	proc_idx = priv->tx.proc_idx;
> > +	done_idx = priv->tx.done_idx;
> > +	ndesc = priv->tx.ndesc;
> > +	freepkt = ((done_idx + ndesc - 1) - proc_idx) % ndesc;
> > +
> > +	/* not enough entry, then we stop queue */
> > +	if (unlikely(freepkt < 2)) {
> > +		netif_stop_queue(ndev);
> > +		if (unlikely(freepkt < 1))
> > +			return NETDEV_TX_BUSY;
> 
> This looks wrong, why are you checking first for less than 2
> descriptors, and if there is none, NETDEV_TX_BUSY? If you need 2 slots
> to complete a transmision, stop the transmit queue and return
> NETDEV_TX_BUSY.

This code is misleading and I have to fix this.
The device needs a slot to complete a transmission.

> > +	}
> > +
> > +	priv->tx.desc[proc_idx].skbs = skb;
> > +
> > +	/* add padding for short packet */
> > +	if (skb_padto(skb, ETH_ZLEN)) {
> > +		dev_kfree_skb_any(skb);
> > +		return NETDEV_TX_OK;
> > +	}
> 
> skb_padto() frees the SKB in case of error, that would lead to a double
> free here.

Ah, it occurs double free. I'll fix it.

> > +
> > +	buffptr = skb->data - NET_IP_ALIGN;
> > +	len = max_t(unsigned int, ETH_ZLEN, skb->len);
> 
> If you use skb_put_padto() if padding was necessary skb->len will be at
> least ETH_ZLEN, so you can remove this.

I see. It's reasonable.

> > +
> > +	paddr = ave_dma_map(ndev, &priv->tx.desc[proc_idx], buffptr,
> > +			    len + NET_IP_ALIGN, DMA_TO_DEVICE);
> 
> As mentioned before you can't assume this will never fail.

Okay, I'll rewrite it in consideration of error case.

> > +	paddr += NET_IP_ALIGN;
> > +
> > +	/* set buffer address to descriptor */
> > +	ave_wdesc_addr(ndev, AVE_DESCID_TX, proc_idx, 4, paddr);
> 
> Also mentioned in the other email, make this 4 a constant so we know
> it's an offset and not a length.

I see.

> > +
> > +	/* set flag and length to send */
> > +	cmdsts = AVE_STS_OWN | AVE_STS_1ST | AVE_STS_LAST
> > +		| (len & AVE_STS_PKTLEN_TX);
> 
> AVE_STS_PKTLEN_TX would be better named with a _MASK suffix.

Yes.

> > +
> > +	/* set interrupt per AVE_FORCE_TXINTCNT or when queue is stopped */
> > +	if (!(proc_idx % AVE_FORCE_TXINTCNT) || netif_queue_stopped(ndev))
> > +		cmdsts |= AVE_STS_INTR;
> > +
> > +	/* disable checksum calculation when skb doesn't calurate checksum */
> > +	if (skb->ip_summed == CHECKSUM_NONE ||
> > +	    skb->ip_summed == CHECKSUM_UNNECESSARY)
> > +		cmdsts |= AVE_STS_NOCSUM;
> > +
> > +	/* set cmdsts */
> > +	ave_wdesc(ndev, AVE_DESCID_TX, proc_idx, 0, cmdsts);
> > +
> > +	priv->tx.proc_idx = (proc_idx + 1) % ndesc;
> 
> You should also check the ring space after transmission and assert flow
> control on the transmit queue if needed.

Okay, I'll add this.

> > +
> > +	return NETDEV_TX_OK;
> > +}
> 
> [snip]
> 
> > +static struct net_device_stats *ave_stats(struct net_device *ndev)
> > +{
> > +	struct ave_private *priv = netdev_priv(ndev);
> > +	u32 drop_num = 0;
> > +
> > +	priv->stats.rx_errors = ave_r32(ndev, AVE_BFCR);
> > +
> > +	drop_num += ave_r32(ndev, AVE_RX0OVFFC);
> > +	drop_num += ave_r32(ndev, AVE_SN5FC);
> > +	drop_num += ave_r32(ndev, AVE_SN6FC);
> > +	drop_num += ave_r32(ndev, AVE_SN7FC);
> > +	priv->stats.rx_dropped = drop_num;
> > +
> 
> You should consider switching to 64-bit statistics, this requires a
> little bit more work for 32-bit hosts (see
> include/linux/u64_stats_sync.h) but this allows you to keep statistics
> around above 4GB.

I see.
I'll refer to this header and its examples, and rewrite it to be suitable
for 32-bit and 64-bit hosts.

> 
> > +	return &priv->stats;
> > +}
> > +-- 
> Florian

---
Best Regards,
Kunihiko Hayashi