netdev - Re: [PATCH net-next v2 2/4] net: stmmac: call phylink_carrier

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Message-ID: <ed54d4e5-ecc3-4327-8739-3d41ca41211e@lunn.ch>
Date: Fri, 2 May 2025 17:29:21 +0200
From: Andrew Lunn <andrew@...n.ch>
To: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>, bpf@...r.kernel.org,
	Daniel Borkmann <daniel@...earbox.net>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Jon Hunter <jonathanh@...dia.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-stm32@...md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@...il.com>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>,
	Thierry Reding <treding@...dia.com>
Subject: Re: [PATCH net-next v2 2/4] net: stmmac: call phylink_carrier_*() in
 XDP functions

On Fri, May 02, 2025 at 02:35:36PM +0100, Russell King (Oracle) wrote:
> Phylink does not permit drivers to mess with the netif carrier, as
> this will de-synchronise phylink with the MAC driver. Moreover,
> setting and clearing the TE and RE bits via stmmac_mac_set() in this
> path is also wrong as the link may not be up.
> 
> Replace the netif_carrier_on(), netif_carrier_off() and
> stmmac_mac_set() calls with the appropriate phylink_carrier_block() and
> phylink_carrier_unblock() calls, thereby allowing phylink to manage the
> netif carrier and TE/RE bits through the .mac_link_up() and
> .mac_link_down() methods.
> 
> This change will have the side effect of printing link messages to
> the kernel log, even though the physical link hasn't changed state.
> This matches the carrier state that userspace sees, which has always
> "bounced".
> 
> Note that RE should only be set after the DMA is ready to avoid the
> receive FIFO between the MAC and DMA blocks overflowing, so
> phylink_start() needs to be placed after DMA has been started.
> 
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> ---
>  .../net/ethernet/stmicro/stmmac/stmmac_main.c | 20 +++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index f59a2363f150..ac27ea679b23 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -6922,6 +6922,11 @@ void stmmac_xdp_release(struct net_device *dev)
>  	/* Ensure tx function is not running */
>  	netif_tx_disable(dev);
>  
> +	/* Take down the software link. stmmac_xdp_open() must be called after
> +	 * this function to release this block.
> +	 */
> +	phylink_carrier_block(priv->phylink);
> +
>  	/* Disable NAPI process */
>  	stmmac_disable_all_queues(priv);
>  
> @@ -6937,14 +6942,10 @@ void stmmac_xdp_release(struct net_device *dev)
>  	/* Release and free the Rx/Tx resources */
>  	free_dma_desc_resources(priv, &priv->dma_conf);
>  
> -	/* Disable the MAC Rx/Tx */
> -	stmmac_mac_set(priv, priv->ioaddr, false);
> -
>  	/* set trans_start so we don't get spurious
>  	 * watchdogs during reset
>  	 */
>  	netif_trans_update(dev);
> -	netif_carrier_off(dev);
>  }
>  

>  int stmmac_xdp_open(struct net_device *dev)
> @@ -7026,25 +7027,28 @@ int stmmac_xdp_open(struct net_device *dev)
>  		hrtimer_setup(&tx_q->txtimer, stmmac_tx_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
>  	}
>  
> -	/* Enable the MAC Rx/Tx */
> -	stmmac_mac_set(priv, priv->ioaddr, true);
> -
>  	/* Start Rx & Tx DMA Channels */
>  	stmmac_start_all_dma(priv);
>  
> +	/* Allow phylink to bring the software link back up.
> +	 * stmmac_xdp_release() must have been called prior to this.
> +	 */

This is counter intuitive. Why is release called before open?

Looking into stmmac_xdp_set_prog() i think i get it. Even if there is
not a running XDP prog, stmmac_xdp_release() is called, and then
stmmac_xdp_open().

Maybe these two functions need better names? prepare and commit?

      Andrew