netdev - Re: [PATCH net-next] net: phy: phy_link_topology: Handle NULL topologies

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Message-ID: <c37482d9-f97b-4f9a-8a2d-efde1a654514@gmail.com>
Date: Fri, 12 Apr 2024 15:07:46 +0200
From: Heiner Kallweit <hkallweit1@...il.com>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>, davem@...emloft.net
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 thomas.petazzoni@...tlin.com, Andrew Lunn <andrew@...n.ch>,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, Russell King <linux@...linux.org.uk>,
 linux-arm-kernel@...ts.infradead.org,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Herve Codina <herve.codina@...tlin.com>,
 Florian Fainelli <f.fainelli@...il.com>,
 Vladimir Oltean <vladimir.oltean@....com>,
 Köry Maincent <kory.maincent@...tlin.com>,
 Jesse Brandeburg <jesse.brandeburg@...el.com>, Marek Behún
 <kabel@...nel.org>, Piergiorgio Beruto <piergiorgio.beruto@...il.com>,
 Oleksij Rempel <o.rempel@...gutronix.de>,
 Nicolò Veronese <nicveronese@...il.com>,
 Simon Horman <horms@...nel.org>, mwojtas@...omium.org,
 Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH net-next] net: phy: phy_link_topology: Handle NULL
 topologies

On 12.04.2024 12:46, Maxime Chevallier wrote:
> In situations where phylib is a module, the topology can be NULL as it's
> not initialized at netdev creation.
> 

What we see here is a bigger drawback of IS_REACHABLE(). For phylib it's
false from net core, but true from r8169 driver. So topo_create is a stub,
but topo_add is not. IS_REACHABLE() hides dependencies.

topo_create et al don't really use something from phylib.
Therefore, could/should it be moved to net core?
At least for topo_create this would resolve the dependency.

We could also add a config symbol and the PHY topology an optional
extension of net core.

> Allow passing a NULL topology pointer to phy_link_topo helpers.
> 
> Signed-off-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
> 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/
> ---
> 
> Hi,
> 
> This patch fixes a commit that is in net-next, hence the net-next tag and the
> lack of "Fixes" tag.
> 
> Nathan, Heiner, can you confirm this solves what you're seeing ?
> 
> I think we can improve on this solution by moving the topology init at
> the first PHY insertion and clearing it at netdev destruction.
> 
> Maxime
> 
>  drivers/net/phy/phy_link_topology.c | 10 +++++++++-
>  include/linux/phy_link_topology.h   |  7 ++++++-
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/phy_link_topology.c b/drivers/net/phy/phy_link_topology.c
> index 985941c5c558..0f3973f07fac 100644
> --- a/drivers/net/phy/phy_link_topology.c
> +++ b/drivers/net/phy/phy_link_topology.c
> @@ -42,6 +42,9 @@ int phy_link_topo_add_phy(struct phy_link_topology *topo,
>  	struct phy_device_node *pdn;
>  	int ret;
>  
> +	if (!topo)
> +		return 0;
> +
>  	pdn = kzalloc(sizeof(*pdn), GFP_KERNEL);
>  	if (!pdn)
>  		return -ENOMEM;
> @@ -93,7 +96,12 @@ EXPORT_SYMBOL_GPL(phy_link_topo_add_phy);
>  void phy_link_topo_del_phy(struct phy_link_topology *topo,
>  			   struct phy_device *phy)
>  {
> -	struct phy_device_node *pdn = xa_erase(&topo->phys, phy->phyindex);
> +	struct phy_device_node *pdn;
> +
> +	if (!topo)
> +		return;
> +
> +	pdn = xa_erase(&topo->phys, phy->phyindex);
>  
>  	/* We delete the PHY from the topology, however we don't re-set the
>  	 * phy->phyindex field. If the PHY isn't gone, we can re-assign it the
> diff --git a/include/linux/phy_link_topology.h b/include/linux/phy_link_topology.h
> index 6b79feb607e7..21ca78127d0f 100644
> --- a/include/linux/phy_link_topology.h
> +++ b/include/linux/phy_link_topology.h
> @@ -40,7 +40,12 @@ struct phy_link_topology {
>  static inline struct phy_device *
>  phy_link_topo_get_phy(struct phy_link_topology *topo, u32 phyindex)
>  {
> -	struct phy_device_node *pdn = xa_load(&topo->phys, phyindex);
> +	struct phy_device_node *pdn;
> +
> +	if (!topo)
> +		return NULL;
> +
> +	pdn = xa_load(&topo->phys, phyindex);
>  
>  	if (pdn)
>  		return pdn->phy;