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

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Date: Sat, 27 Apr 2024 21:34:21 +0200
From: Heiner Kallweit <hkallweit1@...il.com>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: davem@...emloft.net, 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>, Antoine Tenart <atenart@...nel.org>
Subject: Re: [PATCH net-next] net: phy: phy_link_topology: Handle NULL
 topologies

On 12.04.2024 15:23, Maxime Chevallier wrote:
> Hello Heiner,
> 
> On Fri, 12 Apr 2024 15:07:46 +0200
> Heiner Kallweit <hkallweit1@...il.com> wrote:
> 
>> 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?
> 
> That's a valid point, and a better solution indeed.
> 
>> 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.
> 
> That could be a thing indeed. It could be selected by phylib then, I
> don't see it being a user-controlled option, as this would make it very
> confusing for users to only be able to see when there are mutiple PHYs
> on the link when the relevant option is enabled (but I might be wrong).
> 
AFAIK the issue still exists on net-next. Are you going to submit
an updated version?

> Maxime
> 
>>
>>> 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;  
>>
>