drm/i915: Add a way to test the modeset done during gpu reset, v3.

Add force_reset_modeset_test as a parameter to force the modeset path during gpu reset.
This allows a IGT test to set the knob and trigger a hang to force the gpu reset,
even on platforms that wouldn't otherwise require it.

Changes since v1:
- Split out fix to separate commit.
Changes since v2:
- This commit is purely about force_reset_modeset_test now.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Testcase: drv_hangman.reset-with-forced-modeset
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470428910-12125-3-git-send-email-ville.syrjala@linux.intel.com
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/i915_params.c

@@ -45,6 +45,7 @@ struct i915_params i915 __read_mostly = {
 	.fastboot = 0,
 	.prefault_disable = 0,
 	.load_detect_test = 0,
+	.force_reset_modeset_test = 0,
 	.reset = true,
 	.invert_brightness = 0,
 	.disable_display = 0,
@@ -161,6 +162,11 @@ MODULE_PARM_DESC(load_detect_test,
 	"Force-enable the VGA load detect code for testing (default:false). "
 	"For developers only.");
 
+module_param_named_unsafe(force_reset_modeset_test, i915.force_reset_modeset_test, bool, 0600);
+MODULE_PARM_DESC(force_reset_modeset_test,
+	"Force a modeset during gpu reset for testing (default:false). "
+	"For developers only.");
+
 module_param_named_unsafe(invert_brightness, i915.invert_brightness, int, 0600);
 MODULE_PARM_DESC(invert_brightness,
 	"Invert backlight brightness "

drivers/gpu/drm/i915/i915_params.h

@@ -57,6 +57,7 @@ struct i915_params {
 	bool fastboot;
 	bool prefault_disable;
 	bool load_detect_test;
+	bool force_reset_modeset_test;
 	bool reset;
 	bool disable_display;
 	bool verbose_state_checks;

drivers/gpu/drm/i915/intel_display.c

@@ -3161,7 +3161,8 @@ void intel_prepare_reset(struct drm_i915_private *dev_priv)
 	}
 
 	/* reset doesn't touch the display, but flips might get nuked anyway, */
-	if (INTEL_GEN(dev_priv) >= 5 || IS_G4X(dev_priv))
+	if (!i915.force_reset_modeset_test &&
+	    (INTEL_GEN(dev_priv) >= 5 || IS_G4X(dev_priv)))
 		return;
 
 	/*
@@ -3212,16 +3213,22 @@ void intel_finish_reset(struct drm_i915_private *dev_priv)
 
 	/* reset doesn't touch the display */
 	if (INTEL_GEN(dev_priv) >= 5 || IS_G4X(dev_priv)) {
-		/*
-		 * Flips in the rings have been nuked by the reset,
-		 * so update the base address of all primary
-		 * planes to the the last fb to make sure we're
-		 * showing the correct fb after a reset.
-		 *
-		 * FIXME: Atomic will make this obsolete since we won't schedule
-		 * CS-based flips (which might get lost in gpu resets) any more.
-		 */
-		intel_update_primary_planes(dev);
+		if (!state) {
+			/*
+			 * Flips in the rings have been nuked by the reset,
+			 * so update the base address of all primary
+			 * planes to the the last fb to make sure we're
+			 * showing the correct fb after a reset.
+			 *
+			 * FIXME: Atomic will make this obsolete since we won't schedule
+			 * CS-based flips (which might get lost in gpu resets) any more.
+			 */
+			intel_update_primary_planes(dev);
+		} else {
+			ret = __intel_display_resume(dev, state);
+			if (ret)
+				DRM_ERROR("Restoring old state failed with %i\n", ret);
+		}
 	} else {
 		/*
 		 * The display has been reset as well,