[Intel-gfx] [PATCH] drm/i915: Reject excessive dotclocks early

[Ville Syrjala]

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

Make sure modes with crazy big dotclocks are rejected early,
so as to not cause problems for subsequent code via integer
overflows and whatnot.

These would eventually be rejected in intel_crtc_compute_pipe_mode()
but that is now too late as we do the clock computations a bit
earlier than that. And we don't want to just reorder the two since
we still want to check the final computed dotclock against the
hardware limit to make sure we didn't end up above the limit due
to rounding/etc.

Fixes: 0ff0e219d9b8 ("drm/i915: Compute clocks earlier")
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index eb8eaeb19881..04e8fa953bc7 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -8130,6 +8130,17 @@ static void intel_setup_outputs(struct drm_i915_private *dev_priv)
 	drm_helper_move_panel_connectors_to_head(&dev_priv->drm);
 }
 
+static int max_dotclock(struct drm_i915_private *i915)
+{
+	int max_dotclock = i915->max_dotclk_freq;
+
+	/* icl+ might use bigjoiner */
+	if (DISPLAY_VER(i915) >= 11)
+		max_dotclock *= 2;
+
+	return max_dotclock;
+}
+
 static enum drm_mode_status
 intel_mode_valid(struct drm_device *dev,
 		 const struct drm_display_mode *mode)
@@ -8167,6 +8178,13 @@ intel_mode_valid(struct drm_device *dev,
 			   DRM_MODE_FLAG_CLKDIV2))
 		return MODE_BAD;
 
+	/*
+	 * Reject clearly excessive dotclocks early to
+	 * avoid having to worry about huge integers later.
+	 */
+	if (mode->clock > max_dotclock(dev_priv))
+		return MODE_CLOCK_HIGH;
+
 	/* Transcoder timing limits */
 	if (DISPLAY_VER(dev_priv) >= 11) {
 		hdisplay_max = 16384;
-- 
2.35.1