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.

Signed-off-by: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
Testcase: drv_hangman.reset-with-forced-modeset
---
 drivers/gpu/drm/i915/i915_params.c   |  6 ++++++
 drivers/gpu/drm/i915/i915_params.h   |  1 +
 drivers/gpu/drm/i915/intel_display.c | 42 ++++++++++++++++++++++++------------
 3 files changed, 35 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_params.c 
b/drivers/gpu/drm/i915/i915_params.c
index 1779f02e6df8..80ce581793dc 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/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,
@@ -158,6 +159,11 @@ 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 "
diff --git a/drivers/gpu/drm/i915/i915_params.h 
b/drivers/gpu/drm/i915/i915_params.h
index 02bc27804291..3934c4300427 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -55,6 +55,7 @@ struct i915_params {
        bool fastboot;
        bool prefault_disable;
        bool load_detect_test;
+       bool force_reset_modeset_test;
        bool reset;
        bool disable_display;
        bool enable_guc_submission;
diff --git a/drivers/gpu/drm/i915/intel_display.c 
b/drivers/gpu/drm/i915/intel_display.c
index 2f76efc86417..faf2da08778f 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3160,6 +3160,7 @@ __intel_display_resume(struct drm_device *dev,
 
 void intel_prepare_reset(struct drm_device *dev)
 {
+       bool requires_display_reset = true;
        struct drm_atomic_state *state;
        struct drm_modeset_acquire_ctx *pctx;
        int ret;
@@ -3169,8 +3170,12 @@ void intel_prepare_reset(struct drm_device *dev)
                return;
 
        /* reset doesn't touch the display */
-       if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
-               return;
+       if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev)) {
+               if (!i915.force_reset_modeset_test)
+                       return;
+
+               requires_display_reset = false;
+       }
 
        drm_modeset_lock_all(dev);
        pctx = dev->mode_config.acquire_ctx;
@@ -3199,12 +3204,15 @@ void intel_prepare_reset(struct drm_device *dev)
 
 err:
        drm_atomic_state_free(state);
+       if (!requires_display_reset)
+               drm_modeset_unlock_all(dev);
 }
 
 void intel_finish_reset(struct drm_device *dev)
 {
        struct drm_i915_private *dev_priv = to_i915(dev);
        struct drm_atomic_state *state = dev_priv->modeset_restore_state;
+       bool hpd_init;
        int ret;
 
        /*
@@ -3220,22 +3228,27 @@ void intel_finish_reset(struct drm_device *dev)
 
        /* reset doesn't touch the display */
        if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev)) {
-               /*
-                * 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);
-               return;
+               hpd_init = false;
+
+               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);
+                       return;
+               }
        } else {
                /*
                 * The display has been reset as well,
                 * so need a full re-initialization.
                 */
+               hpd_init = true;
                intel_runtime_pm_disable_interrupts(dev_priv);
                intel_runtime_pm_enable_interrupts(dev_priv);
 
@@ -3255,7 +3268,8 @@ void intel_finish_reset(struct drm_device *dev)
        if (ret)
                DRM_ERROR("Restoring old state failed with %i\n", ret);
 
-       intel_hpd_init(dev_priv);
+       if (hpd_init)
+               intel_hpd_init(dev_priv);
 
        drm_modeset_unlock_all(dev);
 }
-- 
2.1.0

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