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| 2 |
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| 3 | =====================
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| 4 | Devicetree Changesets
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| 5 | =====================
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| 6 |
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| 7 | A Devicetree changeset is a method which allows one to apply changes
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| 8 | in the live tree in such a way that either the full set of changes
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| 9 | will be applied, or none of them will be. If an error occurs partway
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| 10 | through applying the changeset, then the tree will be rolled back to the
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| 11 | previous state. A changeset can also be removed after it has been
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| 12 | applied.
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| 13 |
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| 14 | When a changeset is applied, all of the changes get applied to the tree
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| 15 | at once before emitting OF_RECONFIG notifiers. This is so that the
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| 16 | receiver sees a complete and consistent state of the tree when it
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| 17 | receives the notifier.
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| 18 |
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| 19 | The sequence of a changeset is as follows.
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| 20 |
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| 21 | 1. of_changeset_init() - initializes a changeset
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| 22 |
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| 23 | 2. A number of DT tree change calls, of_changeset_attach_node(),
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| 24 | of_changeset_detach_node(), of_changeset_add_property(),
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| 25 | of_changeset_remove_property, of_changeset_update_property() to prepare
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| 26 | a set of changes. No changes to the active tree are made at this point.
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| 27 | All the change operations are recorded in the of_changeset 'entries'
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| 28 | list.
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| 29 |
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| 30 | 3. of_changeset_apply() - Apply the changes to the tree. Either the
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| 31 | entire changeset will get applied, or if there is an error the tree will
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| 32 | be restored to the previous state. The core ensures proper serialization
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| 33 | through locking. An unlocked version __of_changeset_apply is available,
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| 34 | if needed.
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| 35 |
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| 36 | If a successfully applied changeset needs to be removed, it can be done
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| 37 | with of_changeset_revert().
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