drm/i915: Put future HW and their uAPIs under STAGING & BROKEN

We would like some freedom to break the user API/ABI for future HW but
yet still expose the driver for upstream development on that HW.
Currently, we have the i915.force_probe module parameter to avoid binding
to HW while the driver is under development, but that is still a little
too soft with respect to the stringent no-regression rules if we also
plan to be redesigning the uAPI to go along with the new HW.

To allow the uAPI to be changed during development, only expose that API
and in development HW under STAGING (and BROKEN). Hopefully, making it
explicit that such interfaces to that HW are under development and not
to be blindly enabled by distributions.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191027154314.11139-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/Kconfig

@@ -148,3 +148,9 @@ menu "drm/i915 Profile Guided Optimisation"
 	depends on DRM_I915
 	source "drivers/gpu/drm/i915/Kconfig.profile"
 endmenu
+
+menu "drm/i915 Unstable Evolution"
+	visible if EXPERT && STAGING && BROKEN
+	depends on DRM_I915
+	source "drivers/gpu/drm/i915/Kconfig.unstable"
+endmenu

drivers/gpu/drm/i915/Kconfig.debug

@@ -36,6 +36,7 @@ config DRM_I915_DEBUG
 	select DRM_I915_SELFTEST
 	select DRM_I915_DEBUG_RUNTIME_PM
 	select DRM_I915_DEBUG_MMIO
+	select BROKEN # for prototype uAPI
 	default n
 	help
 	  Choose this option to turn on extra driver debugging that may affect

drivers/gpu/drm/i915/Kconfig.unstable

+# SPDX-License-Identifier: GPL-2.0-only
+config DRM_I915_UNSTABLE
+	bool "Enable unstable API for early prototype development"
+	depends on EXPERT
+	depends on STAGING
+	depends on BROKEN # should never be enabled by distros!
+	# We use the dependency on !COMPILE_TEST to not be enabled in
+	# allmodconfig or allyesconfig configurations
+	depends on !COMPILE_TEST
+	default n
+	help
+	  Enable prototype uAPI under general discussion before they are
+	  finalized. Such prototypes may be withdrawn or substantially
+	  changed before release. They are only enabled here so that a wide
+	  number of interested parties (userspace driver developers) can
+	  verify that the uAPI meet their expectations. These uAPI should
+	  never be used in production.
+
+	  Recommended for driver developers _only_.
+
+	  If in the slightest bit of doubt, say "N".