[Intel-gfx] [PATCH] RFC drm/i915: Put future HW and their uAPIs under STAGING & BROKEN

[Chris Wilson]

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 at chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Dave Airlie <airlied at redhat.com>
---
 drivers/gpu/drm/i915/Kconfig.debug       | 15 +++++++++++++++
 drivers/gpu/drm/i915/i915_gem.c          | 10 ++++++++++
 drivers/gpu/drm/i915/intel_device_info.h |  1 +
 3 files changed, 26 insertions(+)

diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
index 00786a142ff0..7707d1230b85 100644
--- a/drivers/gpu/drm/i915/Kconfig.debug
+++ b/drivers/gpu/drm/i915/Kconfig.debug
@@ -36,6 +36,9 @@ config DRM_I915_DEBUG
 	select DRM_I915_SELFTEST
 	select DRM_I915_DEBUG_RUNTIME_PM
 	select DRM_I915_DEBUG_MMIO
+	select STAGING
+	select BROKEN
+	select DRM_I915_DEBUG_EARLY_API
         default n
         help
           Choose this option to turn on extra driver debugging that may affect
@@ -212,3 +215,15 @@ config DRM_I915_DEBUG_RUNTIME_PM
 	  driver loading, suspend and resume operations.
 
 	  If in doubt, say "N"
+
+config DRM_I915_DEBUG_EARLY_API
+	bool "Expose new HW uAPIs for early testing"
+	depends on DRM_I915
+	depends on STAGING
+	depends on BROKEN
+	default n
+	help
+	  Expose in-development uAPI for early testing on HW. Such uAPI
+	  will likely subtly change before release and must not be relied upon.
+
+	  If in doubt, say "N"
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index bb39c64a0a17..eab2219d7a50 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1344,6 +1344,15 @@ int i915_gem_init(struct drm_i915_private *dev_priv)
 {
 	int ret;
 
+	if (INTEL_INFO(dev_priv)->early_render_uapi) {
+		if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_EARLY_API)) {
+			ret = -EIO;
+			goto err_disable;
+		}
+
+		add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+	}
+
 	/* We need to fallback to 4K pages if host doesn't support huge gtt. */
 	if (intel_vgpu_active(dev_priv) && !intel_vgpu_has_huge_gtt(dev_priv))
 		mkwrite_device_info(dev_priv)->page_sizes =
@@ -1476,6 +1485,7 @@ int i915_gem_init(struct drm_i915_private *dev_priv)
 		intel_timelines_fini(dev_priv);
 	}
 
+err_disable:
 	if (ret == -EIO) {
 		/*
 		 * Allow engines or uC initialisation to fail by marking the GPU
diff --git a/drivers/gpu/drm/i915/intel_device_info.h b/drivers/gpu/drm/i915/intel_device_info.h
index 92e0c2e0954c..5931f619e66b 100644
--- a/drivers/gpu/drm/i915/intel_device_info.h
+++ b/drivers/gpu/drm/i915/intel_device_info.h
@@ -107,6 +107,7 @@ enum intel_ppgtt_type {
 	func(is_mobile); \
 	func(is_lp); \
 	func(require_force_probe); \
+	func(early_render_uapi); \
 	/* Keep has_* in alphabetical order */ \
 	func(has_64bit_reloc); \
 	func(gpu_reset_clobbers_display); \
-- 
2.23.0