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Date: Wed, 8 May 2024 07:44:22 +0200
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From: Heiner Kallweit <hkallweit1@gmail.com>
Subject: Re: [PATCH net-next 2/2] net: phy: phy_link_topology: Lazy-initialize
 the link topology
To: Maxime Chevallier <maxime.chevallier@bootlin.com>, davem@davemloft.net
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
 thomas.petazzoni@bootlin.com, Andrew Lunn <andrew@lunn.ch>,
 Jakub Kicinski <kuba@kernel.org>, Eric Dumazet <edumazet@google.com>,
 Paolo Abeni <pabeni@redhat.com>, Russell King <linux@armlinux.org.uk>,
 linux-arm-kernel@lists.infradead.org,
 Christophe Leroy <christophe.leroy@csgroup.eu>,
 Herve Codina <herve.codina@bootlin.com>,
 Florian Fainelli <f.fainelli@gmail.com>,
 Vladimir Oltean <vladimir.oltean@nxp.com>,
 =?UTF-8?Q?K=C3=B6ry_Maincent?= <kory.maincent@bootlin.com>,
 Jesse Brandeburg <jesse.brandeburg@intel.com>, =?UTF-8?Q?Marek_Beh=C3=BAn?=
 <kabel@kernel.org>, Piergiorgio Beruto <piergiorgio.beruto@gmail.com>,
 Oleksij Rempel <o.rempel@pengutronix.de>,
 =?UTF-8?Q?Nicol=C3=B2_Veronese?= <nicveronese@gmail.com>,
 Simon Horman <horms@kernel.org>, mwojtas@chromium.org,
 Nathan Chancellor <nathan@kernel.org>, Antoine Tenart <atenart@kernel.org>
References: <20240507102822.2023826-1-maxime.chevallier@bootlin.com>
 <20240507102822.2023826-3-maxime.chevallier@bootlin.com>
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In-Reply-To: <20240507102822.2023826-3-maxime.chevallier@bootlin.com>
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On 07.05.2024 12:28, Maxime Chevallier wrote:
> Having the net_device's init path for the link_topology depend on
> IS_REACHABLE(PHYLIB)-protected helpers triggers errors when modules are being
> built with phylib as a module as-well, as they expect netdev->link_topo
> to be initialized.
> 
> Move the link_topo initialization at the first PHY insertion, which will
> both improve the memory usage, and make the behaviour more predicatble
> and robust.
> 
> Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
> Fixes: 6916e461e793 ("net: phy: Introduce ethernet link topology representation")
> Closes: https://lore.kernel.org/netdev/2e11b89d-100f-49e7-9c9a-834cc0b82f97@gmail.com/
> Closes: https://lore.kernel.org/netdev/20240409201553.GA4124869@dev-arch.thelio-3990X/
> ---
>  drivers/net/phy/phy_link_topology.c    | 31 ++++++---------------
>  include/linux/netdevice.h              |  2 ++
>  include/linux/phy_link_topology.h      | 23 ++++++++--------
>  include/linux/phy_link_topology_core.h | 23 +++-------------
>  net/core/dev.c                         | 38 ++++++++++++++++++++++----
>  5 files changed, 58 insertions(+), 59 deletions(-)
> 
> diff --git a/drivers/net/phy/phy_link_topology.c b/drivers/net/phy/phy_link_topology.c
> index 0e36bd7c15dc..b1aba9313e73 100644
> --- a/drivers/net/phy/phy_link_topology.c
> +++ b/drivers/net/phy/phy_link_topology.c
> @@ -12,29 +12,6 @@
>  #include <linux/rtnetlink.h>
>  #include <linux/xarray.h>
>  
> -struct phy_link_topology *phy_link_topo_create(struct net_device *dev)
> -{
> -	struct phy_link_topology *topo;
> -
> -	topo = kzalloc(sizeof(*topo), GFP_KERNEL);
> -	if (!topo)
> -		return ERR_PTR(-ENOMEM);
> -
> -	xa_init_flags(&topo->phys, XA_FLAGS_ALLOC1);
> -	topo->next_phy_index = 1;
> -
> -	return topo;
> -}
> -
> -void phy_link_topo_destroy(struct phy_link_topology *topo)
> -{
> -	if (!topo)
> -		return;
> -
> -	xa_destroy(&topo->phys);
> -	kfree(topo);
> -}
> -
>  int phy_link_topo_add_phy(struct net_device *dev,
>  			  struct phy_device *phy,
>  			  enum phy_upstream upt, void *upstream)
> @@ -43,6 +20,14 @@ int phy_link_topo_add_phy(struct net_device *dev,
>  	struct phy_device_node *pdn;
>  	int ret;
>  
> +	if (!topo) {
> +		ret = netdev_alloc_phy_link_topology(dev);

This function is implemented in net core, but used only here.
So move the implementation here?

> +		if (ret)
> +			return ret;
> +
> +		topo = dev->link_topo;
> +	}
> +
>  	pdn = kzalloc(sizeof(*pdn), GFP_KERNEL);
>  	if (!pdn)
>  		return -ENOMEM;
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index cf261fb89d73..25a0a77cfadc 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -4569,6 +4569,8 @@ void __hw_addr_unsync_dev(struct netdev_hw_addr_list *list,
>  					const unsigned char *));
>  void __hw_addr_init(struct netdev_hw_addr_list *list);
>  
> +int netdev_alloc_phy_link_topology(struct net_device *dev);
> +
>  /* Functions used for device addresses handling */
>  void dev_addr_mod(struct net_device *dev, unsigned int offset,
>  		  const void *addr, size_t len);
> diff --git a/include/linux/phy_link_topology.h b/include/linux/phy_link_topology.h
> index 166a01710aa2..3501f9a9e932 100644
> --- a/include/linux/phy_link_topology.h
> +++ b/include/linux/phy_link_topology.h
> @@ -32,10 +32,12 @@ struct phy_device_node {
>  	struct phy_device *phy;
>  };
>  
> -struct phy_link_topology {
> -	struct xarray phys;
> -	u32 next_phy_index;
> -};
> +#if IS_ENABLED(CONFIG_PHYLIB)
> +int phy_link_topo_add_phy(struct net_device *dev,
> +			  struct phy_device *phy,
> +			  enum phy_upstream upt, void *upstream);
> +
> +void phy_link_topo_del_phy(struct net_device *dev, struct phy_device *phy);
>  
>  static inline struct phy_device
>  *phy_link_topo_get_phy(struct net_device *dev, u32 phyindex)
> @@ -53,13 +55,6 @@ static inline struct phy_device
>  	return NULL;
>  }
>  
> -#if IS_REACHABLE(CONFIG_PHYLIB)
> -int phy_link_topo_add_phy(struct net_device *dev,
> -			  struct phy_device *phy,
> -			  enum phy_upstream upt, void *upstream);
> -
> -void phy_link_topo_del_phy(struct net_device *dev, struct phy_device *phy);
> -
>  #else
>  static inline int phy_link_topo_add_phy(struct net_device *dev,
>  					struct phy_device *phy,
> @@ -72,6 +67,12 @@ static inline void phy_link_topo_del_phy(struct net_device *dev,
>  					 struct phy_device *phy)
>  {
>  }
> +
> +static inline struct phy_device *
> +phy_link_topo_get_phy(struct net_device *dev, u32 phyindex)
> +{
> +	return NULL;
> +}
>  #endif
>  
>  #endif /* __PHY_LINK_TOPOLOGY_H */
> diff --git a/include/linux/phy_link_topology_core.h b/include/linux/phy_link_topology_core.h
> index 0a6479055745..f9c0520806fb 100644
> --- a/include/linux/phy_link_topology_core.h
> +++ b/include/linux/phy_link_topology_core.h
> @@ -2,24 +2,9 @@
>  #ifndef __PHY_LINK_TOPOLOGY_CORE_H
>  #define __PHY_LINK_TOPOLOGY_CORE_H
>  
> -struct phy_link_topology;
> -
> -#if IS_REACHABLE(CONFIG_PHYLIB)
> -
> -struct phy_link_topology *phy_link_topo_create(struct net_device *dev);
> -void phy_link_topo_destroy(struct phy_link_topology *topo);
> -
> -#else
> -
> -static inline struct phy_link_topology *phy_link_topo_create(struct net_device *dev)
> -{
> -	return NULL;
> -}
> -
> -static inline void phy_link_topo_destroy(struct phy_link_topology *topo)
> -{
> -}
> -
> -#endif
> +struct phy_link_topology {
> +	struct xarray phys;
> +	u32 next_phy_index;
> +};
>  
This is all which is left in this header. As this header is public anyway,
better move this definition to phy_link_topology.h?

>  #endif /* __PHY_LINK_TOPOLOGY_CORE_H */
> diff --git a/net/core/dev.c b/net/core/dev.c
> index d2ce91a334c1..1b4ffc273a04 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10256,6 +10256,35 @@ static void netdev_do_free_pcpu_stats(struct net_device *dev)
>  	}
>  }
>  
> +int netdev_alloc_phy_link_topology(struct net_device *dev)
> +{
> +	struct phy_link_topology *topo;
> +
> +	topo = kzalloc(sizeof(*topo), GFP_KERNEL);
> +	if (!topo)
> +		return -ENOMEM;
> +
> +	xa_init_flags(&topo->phys, XA_FLAGS_ALLOC1);
> +	topo->next_phy_index = 1;
> +
> +	dev->link_topo = topo;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(netdev_alloc_phy_link_topology);
> +
> +static void netdev_free_phy_link_topology(struct net_device *dev)
> +{
> +	struct phy_link_topology *topo = dev->link_topo;
> +
> +	if (!topo)
> +		return;
> +
> +	xa_destroy(&topo->phys);
> +	kfree(topo);
> +	dev->link_topo = NULL;

Give the compiler a chance to remove this function if
CONFIG_PHYLIB isn't enabled.

if (IS_ENABLED(CONFIG_PHYLIB) && topo) {
	xa_destroy(&topo->phys);
	kfree(topo);
	dev->link_topo = NULL;
}

> +}
> +
>  /**
>   * register_netdevice() - register a network device
>   * @dev: device to register
> @@ -10998,11 +11027,6 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
>  #ifdef CONFIG_NET_SCHED
>  	hash_init(dev->qdisc_hash);
>  #endif
> -	dev->link_topo = phy_link_topo_create(dev);
> -	if (IS_ERR(dev->link_topo)) {
> -		dev->link_topo = NULL;
> -		goto free_all;
> -	}
>  
>  	dev->priv_flags = IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM;
>  	setup(dev);
> @@ -11092,7 +11116,9 @@ void free_netdev(struct net_device *dev)
>  	free_percpu(dev->xdp_bulkq);
>  	dev->xdp_bulkq = NULL;
>  
> -	phy_link_topo_destroy(dev->link_topo);
> +#if IS_ENABLED(CONFIG_PHYLIB)
> +	netdev_free_phy_link_topology(dev);
> +#endif
>  
Then the conditional compiling can be removed here.

>  	/*  Compatibility with error handling in drivers */
>  	if (dev->reg_state == NETREG_UNINITIALIZED ||