Partially revert "drm/i915: Use full atomic modeset."

This partially reverts commit 74c090b1.

The DRIVER_ATOMIC cap cannot yet be exported because i915 lacks async
support.
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.c

@@ -1726,7 +1726,7 @@ static int __init i915_init(void)
 	 * to the atomic ioctl and the atomic properties.  Only plane operations on
 	 * a single CRTC will actually work.
 	 */
-	if (driver.driver_features & DRIVER_MODESET)
+	if (i915.nuclear_pageflip)
 		driver.driver_features |= DRIVER_ATOMIC;
 
 	return drm_pci_init(&driver, &i915_pci_driver);

drivers/gpu/drm/i915/i915_drv.h

@@ -2640,6 +2640,7 @@ struct i915_params {
 	int use_mmio_flip;
 	int mmio_debug;
 	bool verbose_state_checks;
+	bool nuclear_pageflip;
 	int edp_vswing;
 };
 extern struct i915_params i915 __read_mostly;

drivers/gpu/drm/i915/i915_params.c

@@ -51,6 +51,7 @@ struct i915_params i915 __read_mostly = {
 	.use_mmio_flip = 0,
 	.mmio_debug = 0,
 	.verbose_state_checks = 1,
+	.nuclear_pageflip = 0,
 	.edp_vswing = 0,
 	.enable_guc_submission = false,
 	.guc_log_level = -1,
@@ -177,6 +178,10 @@ module_param_named(verbose_state_checks, i915.verbose_state_checks, bool, 0600);
 MODULE_PARM_DESC(verbose_state_checks,
 	"Enable verbose logs (ie. WARN_ON()) in case of unexpected hw state conditions.");
 
+module_param_named_unsafe(nuclear_pageflip, i915.nuclear_pageflip, bool, 0600);
+MODULE_PARM_DESC(nuclear_pageflip,
+		 "Force atomic modeset functionality; asynchronous mode is not yet supported. (default: false).");
+
 /* WA to get away with the default setting in VBT for early platforms.Will be removed */
 module_param_named_unsafe(edp_vswing, i915.edp_vswing, int, 0400);
 MODULE_PARM_DESC(edp_vswing,