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docs: net: dsa: document the shutdown behavior

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Document the changes that took place in the DSA core in the blamed
commit.

Fixes: 0650bf52b3 ("net: dsa: be compatible with masters which unregister on shutdown")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Vladimir Oltean 2022-07-16 21:53:31 +03:00 committed by David S. Miller
parent 19b3b13c93
commit 54367831c5
1 changed files with 18 additions and 0 deletions
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18
Documentation/networking/dsa/dsa.rst
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@ -572,6 +572,24 @@ The opposite of registration takes place when calling ``dsa_unregister_switch()`
which removes a switch's ports from the port list of the tree. The entire tree
is torn down when the first switch unregisters.
It is mandatory for DSA switch drivers to implement the ``shutdown()`` callback
of their respective bus, and call ``dsa_switch_shutdown()`` from it (a minimal
version of the full teardown performed by ``dsa_unregister_switch()``).
The reason is that DSA keeps a reference on the master net device, and if the
driver for the master device decides to unbind on shutdown, DSA's reference
will block that operation from finalizing.
Either ``dsa_switch_shutdown()`` or ``dsa_unregister_switch()`` must be called,
but not both, and the device driver model permits the bus' ``remove()`` method
to be called even if ``shutdown()`` was already called. Therefore, drivers are
expected to implement a mutual exclusion method between ``remove()`` and
``shutdown()`` by setting their drvdata to NULL after any of these has run, and
checking whether the drvdata is NULL before proceeding to take any action.
After ``dsa_switch_shutdown()`` or ``dsa_unregister_switch()`` was called, no
further callbacks via the provided ``dsa_switch_ops`` may take place, and the
driver may free the data structures associated with the ``dsa_switch``.
Switch configuration
--------------------