netdev - Re: [RFC PATCH net] net: dsa: tear down devlink port regions when tearing down the devlink port on error

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Date:   Tue, 7 Sep 2021 09:49:48 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Vladimir Oltean <olteanv@...il.com>,
        Leon Romanovsky <leon@...nel.org>,
        Vladimir Oltean <vladimir.oltean@....com>,
        netdev@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>
Subject: Re: [RFC PATCH net] net: dsa: tear down devlink port regions when
 tearing down the devlink port on error



On 9/7/2021 9:43 AM, Andrew Lunn wrote:
> On Tue, Sep 07, 2021 at 08:47:35AM -0700, Florian Fainelli wrote:
>>
>>
>> On 9/7/2021 8:44 AM, Jakub Kicinski wrote:
>>> On Sun, 5 Sep 2021 14:07:35 +0300 Vladimir Oltean wrote:
>>>> Again, fallback but not during devlink port register. The devlink port
>>>> was registered just fine, but our plans changed midway. If you want to
>>>> create a net device with an associated devlink port, first you need to
>>>> create the devlink port and then the net device, then you need to link
>>>> the two using devlink_port_type_eth_set, at least according to my
>>>> understanding.
>>>>
>>>> So the failure is during the creation of the **net device**, we now have a
>>>> devlink port which was originally intended to be of the Ethernet type
>>>> and have a physical flavour, but it will not be backed by any net device,
>>>> because the creation of that just failed. So the question is simply what
>>>> to do with that devlink port.
>>>
>>> Is the failure you're referring to discovered inside the
>>> register_netdevice() call?
>>
>> It is before, at the time we attempt to connect to the PHY device, prior to
>> registering the netdev, we may fail that PHY connection, tearing down the
>> entire switch because of that is highly undesirable.
>>
>> Maybe we should re-order things a little bit and try to register devlink
>> ports only after we successfully registered with the PHY/SFP and prior to
>> registering the netdev?
> 
> Maybe, but it should not really matter. EPROBE_DEFER exists, and can
> happen. The probe can fail for other reasons. All core code should be
> cleanly undoable. Maybe we are pushing it a little by only wanting to
> undo a single port, rather than the whole switch, but still, i would
> make the core handle this, not rearrange the driver. It is not robust
> otherwise.

Well yes, in case my comment was not clear, I was referring to the way 
that DSA register devlink ports, not how the mv88e6xxx driver does it. 
That is assuming that it is possible and there was not a reason for 
configuring the devlink ports ahead of the switch driver coming up.
-- 
Florian