drm/doc: Document feature merge deadlines

The discussion pretty much concluded without objections, let's
document what we agreed on.

Cc'ing linux-doc for the new tag in Documentation/process/index.rst.

Acked-by: Dave Airlie <airlied@gmail.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Dave Airlie <airlied@gmail.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Alex Deucher <alexdeucher@gmail.com>
Cc: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170321155228.30287-1-daniel.vetter@ffwll.ch

Documentation/gpu/introduction.rst

@@ -60,3 +60,28 @@ checkpatch or sparse. We welcome such contributions.
 
 Anyone looking to kick it up a notch can find a list of janitorial tasks on
 the :ref:`TODO list <todo>`.
+
+Contribution Process
+====================
+
+Mostly the DRM subsystem works like any other kernel subsystem, see :ref:`the
+main process guidelines and documentation <process_index>` for how things work.
+Here we just document some of the specialities of the GPU subsystem.
+
+Feature Merge Deadlines
+-----------------------
+
+All feature work must be in the linux-next tree by the -rc6 release of the
+current release cycle, otherwise they must be postponed and can't reach the next
+merge window. All patches must have landed in the drm-next tree by latest -rc7,
+but if your branch is not in linux-next then this must have happened by -rc6
+already.
+
+After that point only bugfixes (like after the upstream merge window has closed
+with the -rc1 release) are allowed. No new platform enabling or new drivers are
+allowed.
+
+This means that there's a blackout-period of about one month where feature work
+can't be merged. The recommended way to deal with that is having a -next tree
+that's always open, but making sure to not feed it into linux-next during the
+blackout period. As an example, drm-misc works like that.

Documentation/process/index.rst

@@ -3,6 +3,7 @@
 	\renewcommand\thesection*
 	\renewcommand\thesubsection*
 
+.. _process_index:
 
 Working with the kernel development community
 =============================================