linux-kernel - Re: [net-next v14 06/12] net: mtip: Add net_device

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Message-ID: <20250709120817.5b2f631a@wsk>
Date: Wed, 9 Jul 2025 12:08:16 +0200
From: Lukasz Majewski <lukma@...x.de>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, davem@...emloft.net, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>, Sascha Hauer
 <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Richard Cochran
 <richardcochran@...il.com>, netdev@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, Stefan Wahren
 <wahrenst@....net>, Simon Horman <horms@...nel.org>
Subject: Re: [net-next v14 06/12] net: mtip: Add net_device_ops functions to
 the L2 switch driver

Hi Paolo,

> On 7/1/25 1:49 PM, Lukasz Majewski wrote:
> > +static netdev_tx_t mtip_start_xmit_port(struct sk_buff *skb,
> > +					struct net_device *dev,
> > int port) +{
> > +	struct mtip_ndev_priv *priv = netdev_priv(dev);
> > +	struct switch_enet_private *fep = priv->fep;
> > +	unsigned short status;
> > +	struct cbd_t *bdp;
> > +	void *bufaddr;
> > +
> > +	spin_lock(&fep->hw_lock);  
> 
> mtip_start_xmit_port() runs with BH disabled. The above lock variant
> is inconsistent with what you use in patch 4.

I've looked into the fec_main.c driver. They use for TX path
__netif_tx_lock(nq, cpu); which is a simple spin_lock(). I've followed
the same approach (as _irqsave() seems to be an overkill).

This function (mtip_start_xmit_port()) is call as a callback from:
.ndo_start_xmit (member of struct net_device_ops).

IIRC net core code provides locking on this call anyway.

> Please be sure to run
> tests vs the next iteration with CONFIG_PROVE_LOCKING enabled.

This is already enabled. Locking in this driver is a bit special, as
one uDMA is used for both ports... (unlikely as in fec_main.c).

> 
> /P
> 




Best regards,

Lukasz Majewski

--

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