[Intel-gfx] [PATCH 4.20 regression fix] drm/i915: Revert "Fix assert_plane() warning on bootup with external display"

[Hans de Goede]

Starting with 4.20-rc1 I'm seeing the LCD screen briefly turn mostly purple
on devices with a DSI panel (seen on 2 different devices with a DSI panel).

This happens both with and without fastboot=1. This is caused by
commit 516a49cc1946 ("drm/i915: Fix assert_plane() warning on bootup with
external display").

And a user commenting on fdo bug 108225 has reported a flicker caused by
the screen briefly turning blank when booting with fastboot=1, which goes
away when reverting this commit.

I believe a revert of the offending commit is the best solution because
the commit introduces a drm_atomic_commit() call in the drivers' probe
path, causing writes to the hardware during probe.
I believe this goes agains the design of the driver which is to only
read-back state on probe and only write to the hardware on the first
commit from the fbcon or userspace.

Instead the assert_plane() problem the commit tried to fix should be fixed
by fixing the state read-back code.

Related: https://bugs.freedesktop.org/show_bug.cgi?id=108225
Cc: Azhar Shaikh <azhar.shaikh at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/i915/intel_display.c | 61 +---------------------------
 1 file changed, 2 insertions(+), 59 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 2107de6da692..03dec1c05652 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -15193,61 +15193,12 @@ static void intel_update_fdi_pll_freq(struct drm_i915_private *dev_priv)
 	DRM_DEBUG_DRIVER("FDI PLL freq=%d\n", dev_priv->fdi_pll_freq);
 }
 
-static int intel_initial_commit(struct drm_device *dev)
-{
-	struct drm_atomic_state *state = NULL;
-	struct drm_modeset_acquire_ctx ctx;
-	struct drm_crtc *crtc;
-	struct drm_crtc_state *crtc_state;
-	int ret = 0;
-
-	state = drm_atomic_state_alloc(dev);
-	if (!state)
-		return -ENOMEM;
-
-	drm_modeset_acquire_init(&ctx, 0);
-
-retry:
-	state->acquire_ctx = &ctx;
-
-	drm_for_each_crtc(crtc, dev) {
-		crtc_state = drm_atomic_get_crtc_state(state, crtc);
-		if (IS_ERR(crtc_state)) {
-			ret = PTR_ERR(crtc_state);
-			goto out;
-		}
-
-		if (crtc_state->active) {
-			ret = drm_atomic_add_affected_planes(state, crtc);
-			if (ret)
-				goto out;
-		}
-	}
-
-	ret = drm_atomic_commit(state);
-
-out:
-	if (ret == -EDEADLK) {
-		drm_atomic_state_clear(state);
-		drm_modeset_backoff(&ctx);
-		goto retry;
-	}
-
-	drm_atomic_state_put(state);
-
-	drm_modeset_drop_locks(&ctx);
-	drm_modeset_acquire_fini(&ctx);
-
-	return ret;
-}
-
 int intel_modeset_init(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct i915_ggtt *ggtt = &dev_priv->ggtt;
 	enum pipe pipe;
 	struct intel_crtc *crtc;
-	int ret;
 
 	dev_priv->modeset_wq = alloc_ordered_workqueue("i915_modeset", 0);
 
@@ -15319,6 +15270,8 @@ int intel_modeset_init(struct drm_device *dev)
 		      INTEL_INFO(dev_priv)->num_pipes > 1 ? "s" : "");
 
 	for_each_pipe(dev_priv, pipe) {
+		int ret;
+
 		ret = intel_crtc_init(dev_priv, pipe);
 		if (ret) {
 			drm_mode_config_cleanup(dev);
@@ -15374,16 +15327,6 @@ int intel_modeset_init(struct drm_device *dev)
 	if (!HAS_GMCH_DISPLAY(dev_priv))
 		sanitize_watermarks(dev);
 
-	/*
-	 * Force all active planes to recompute their states. So that on
-	 * mode_setcrtc after probe, all the intel_plane_state variables
-	 * are already calculated and there is no assert_plane warnings
-	 * during bootup.
-	 */
-	ret = intel_initial_commit(dev);
-	if (ret)
-		DRM_DEBUG_KMS("Initial commit in probe failed.\n");
-
 	return 0;
 }
 
-- 
2.19.1