[Intel-gfx] [PATCH 1/4] drm/i915: Don't clobber M/N values during fastset check

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

We're now calling intel_pipe_config_compare(..., true) uncoditionally
which means we're always going clobber the calculated M/N values with
the old values if the fuzzy M/N check passes. That causes problems
because the fuzzy check allows for a huge difference in the values.

I'm actually tempted to just make the M/N checks exact, but that might
prevent fastboot from kicking in when people want it. So for now let's
overwrite the computed values with the old values only if decide to skip
the modeset.

Cc: stable at vger.kernel.org
Cc: Blubberbub at protonmail.com
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Hans de Goede <hdegoede at redhat.com>
Tested-by: Blubberbub at protonmail.com
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110782
Fixes: d19f958db23c ("drm/i915: Enable fastset for non-boot modesets.")
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 35 +++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 1b1ddb48ca7a..73b3e92b7ed5 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12299,9 +12299,6 @@ intel_compare_link_m_n(const struct intel_link_m_n *m_n,
 			      m2_n2->gmch_m, m2_n2->gmch_n, !adjust) &&
 	    intel_compare_m_n(m_n->link_m, m_n->link_n,
 			      m2_n2->link_m, m2_n2->link_n, !adjust)) {
-		if (adjust)
-			*m2_n2 = *m_n;
-
 		return true;
 	}
 
@@ -13433,6 +13430,32 @@ static int calc_watermark_data(struct intel_atomic_state *state)
 	return 0;
 }
 
+static void intel_crtc_check_fastset(struct intel_crtc_state *old_crtc_state,
+				     struct intel_crtc_state *new_crtc_state)
+{
+	struct drm_i915_private *dev_priv =
+		to_i915(new_crtc_state->base.crtc->dev);
+
+	if (!intel_pipe_config_compare(dev_priv, old_crtc_state,
+				       new_crtc_state, true))
+		return;
+
+	new_crtc_state->base.mode_changed = false;
+	new_crtc_state->update_pipe = true;
+
+	/*
+	 * If we're not doing the full modeset we want to
+	 * keep the current M/N values as they may be
+	 * sufficiently different to the computed values
+	 * to cause problems.
+	 *
+	 * FIXME: should really copy more fuzzy state here
+	 */
+	new_crtc_state->fdi_m_n = old_crtc_state->fdi_m_n;
+	new_crtc_state->dp_m_n = old_crtc_state->dp_m_n;
+	new_crtc_state->dp_m2_n2 = old_crtc_state->dp_m2_n2;
+}
+
 /**
  * intel_atomic_check - validate state object
  * @dev: drm device
@@ -13474,11 +13497,7 @@ static int intel_atomic_check(struct drm_device *dev,
 		if (ret)
 			goto fail;
 
-		if (intel_pipe_config_compare(dev_priv, old_crtc_state,
-					      new_crtc_state, true)) {
-			new_crtc_state->base.mode_changed = false;
-			new_crtc_state->update_pipe = true;
-		}
+		intel_crtc_check_fastset(old_crtc_state, new_crtc_state);
 
 		if (needs_modeset(&new_crtc_state->base))
 			any_ms = true;
-- 
2.21.0