doc: process.rst: Document device tree resync rules

Document the logic of when we do a full resync of the device trees used
by OF_UPSTREAM as well as that cherry-picking is allowed as needed.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>

doc/develop/devicetree/control.rst

@@ -113,9 +113,12 @@ SoC being used via Kconfig and set `DEFAULT_DEVICE_TREE=<vendor>/<name>` when
 prompted by Kconfig.
 
 However, if `dts/upstream/` hasn't yet received devicetree source file for your
-newly added board support then you can add corresponding devicetree source file
-as `arch/<arch>/dts/<name>.dts`. To select that add `# CONFIG_OF_UPSTREAM is not
-set` and set `DEFAULT_DEVICE_TREE=<name>` when prompted by Kconfig.
+newly added board support then one option is that you can add the corresponding
+devicetree source file as `arch/<arch>/dts/<name>.dts`. To select that add `#
+CONFIG_OF_UPSTREAM is not set` and set `DEFAULT_DEVICE_TREE=<name>` when
+prompted by Kconfig. Another option is that you can use use the "pick" option of
+`dts/update-dts-subtree.sh` mentioned above to bring in the commits that you
+need.
 
 This should include your CPU or SoC's devicetree file. On top of that any U-Boot
 specific tweaks (see: :ref:`dttweaks`) can be made for your board.

doc/develop/process.rst

@@ -108,6 +108,19 @@ Differences to the Linux Development Process
   In U-Boot, ``"-rc1"`` will only be released after all (or at least most of
   the) patches that were submitted during the merge window have been applied.
 
+Resyncing of the device tree subtree
+------------------------------------
+
+As explained in :doc:`devicetree/control` some platforms make use of device tree
+files which come from a git subtree that mirrors the Linux Kernel sources
+itself. For our purposes, we only track releases and not release candidates for
+merging in our tree. These merges follow the normal merge window rules.
+
+In the case of specific changes, such as bug fixes or new platform support,
+these can be "cherry-picked" and are subject to the normal merge rules. For
+example, a bug fix can come in later in the window but a full re-sync only
+happens within the merge window itself.
+
 .. _custodians:
 
 Custodians