[PATCH 11/11] drm/i915: Infer vrefresh range for eDP if the EDID omits it

[Ville Syrjala <ville.syrjala@linux.intel.com>]

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

A bunch of machines seem to have eDP panels where the EDID
indicates continuous frequency support but fails to actually
include the range descirptor. This violates the EDID 1.4
spec, but looks like the Windows driver just hacks around
this by just assuming that the panel supports a continuous
refresh rate range that covers all EDID reported modes.

Do the same so that we get VRR support on these machines.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6323
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 45 +++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 8d1559323412..1f3e4824d316 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -5207,6 +5207,49 @@ intel_edp_add_properties(struct intel_dp *intel_dp)
 						       fixed_mode->vdisplay);
 }
 
+/*
+ * Some VRR eDP panels violate the EDID spec and neglect
+ * to include the monitor range descriptor in the EDID.
+ * Cook up the VRR refresh rate limits based on the modes
+ * reported by the panel.
+ */
+static void
+intel_edp_infer_vrr_range(struct intel_connector *connector)
+{
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct drm_display_info *info = &connector->base.display_info;
+	const struct edid *edid = connector->edid;
+	const struct drm_display_mode *mode;
+
+	if (!HAS_VRR(i915))
+		return;
+
+	if (!edid || edid->revision < 4 ||
+	    !(edid->features & DRM_EDID_FEATURE_CONTINUOUS_FREQ) ||
+	    info->vrr_range.min_vfreq || info->vrr_range.max_vfreq)
+		return;
+
+	if (list_empty(&connector->base.probed_modes))
+		return;
+
+	info->vrr_range.min_vfreq = ~0;
+	info->vrr_range.max_vfreq = 0;
+
+	list_for_each_entry(mode, &connector->base.probed_modes, head) {
+		int vrefresh = drm_mode_vrefresh(mode);
+
+		info->vrr_range.min_vfreq = min_t(int, vrefresh,
+						  info->vrr_range.min_vfreq);
+		info->vrr_range.max_vfreq = max_t(int, vrefresh,
+						  info->vrr_range.max_vfreq);
+	}
+
+	drm_dbg_kms(&i915->drm,
+		    "[CONNECTOR:%d:%s] does not report refresh rate range, assuming: %d Hz - %d Hz\n",
+		    connector->base.base.id, connector->base.name,
+		    info->vrr_range.min_vfreq, info->vrr_range.max_vfreq);
+}
+
 static bool intel_edp_init_connector(struct intel_dp *intel_dp,
 				     struct intel_connector *intel_connector)
 {
@@ -5271,6 +5314,8 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
 	}
 	intel_connector->edid = edid;
 
+	intel_edp_infer_vrr_range(intel_connector);
+
 	intel_bios_init_panel(dev_priv, &intel_connector->panel,
 			      encoder->devdata, IS_ERR(edid) ? NULL : edid);
 
-- 
2.35.1