[PATCH v2 2/3] drm/i915: Consult VBT "LVDS config" bits to determine whether internal LVDS is present

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

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

VBT seems to have some bits to tell us whether the internal LVDS port
has something hooked up. In theory one might expect the VBT to not have
a child device for the LVDS port if there's no panel hooked up, but
in practice many VBTs still add the child device. The "LVDS config" bits
seem more reliable though, so let's check those.

So far we've used the "LVDS config" bits to check for eDP support on
ILK+, and disable the internal LVDS when the value is 3. That value
is actually documented as "Both internal LVDS and SDVO LVDS", but in
practice it looks to mean "eDP" on all the ilk+ VBTs I've seen. So let's
keep that interpretation, but for pre-ILK we will consider the value
3 to also indicate the presence of the internal LVDS.

Currently we have 25 DMI matches for the "no internal LVDS" quirk. In an
effort to reduce that let's toss in a WARN when the DMI match and VBT
both tell us that the internal LVDS is not present. The hope is that
people will report a bug, and then we can just nuke the corresponding
entry from the DMI quirk list. Credits to Jani for this idea.

v2: Split the basic int_lvds_support thing to a separate patch (Jani)

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Ondrej Zary <linux@rainbow-software.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105468
References: https://lists.freedesktop.org/archives/intel-gfx/2018-March/158408.html
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_bios.c     | 15 +++++++++++++--
 drivers/gpu/drm/i915/intel_lvds.c     |  5 ++++-
 drivers/gpu/drm/i915/intel_vbt_defs.h |  2 +-
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
index 49c6816d008c..1747fa627a38 100644
--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c
@@ -518,8 +518,19 @@ parse_driver_features(struct drm_i915_private *dev_priv,
 	if (!driver)
 		return;
 
-	if (driver->lvds_config == BDB_DRIVER_FEATURE_EDP)
-		dev_priv->vbt.int_lvds_support = 0;
+	if (INTEL_GEN(dev_priv) >= 5) {
+		/*
+		 * Note that we consider BDB_DRIVER_FEATURE_INT_SDVO_LVDS
+		 * to mean "eDP". The VBT spec doesn't agree with that
+		 * interpretation, but real world VBTs seem to.
+		 */
+		if (driver->lvds_config != BDB_DRIVER_FEATURE_INT_LVDS)
+			dev_priv->vbt.int_lvds_support = 0;
+	} else {
+		if (driver->lvds_config != BDB_DRIVER_FEATURE_INT_LVDS &&
+		    driver->lvds_config != BDB_DRIVER_FEATURE_INT_SDVO_LVDS)
+			dev_priv->vbt.int_lvds_support = 0;
+	}
 
 	DRM_DEBUG_KMS("DRRS State Enabled:%d\n", driver->drrs_enabled);
 	/*
diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
index 05d012358df8..5e5a77927369 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -962,8 +962,11 @@ void intel_lvds_init(struct drm_i915_private *dev_priv)
 		return;
 
 	/* Skip init on machines we know falsely report LVDS */
-	if (dmi_check_system(intel_no_lvds))
+	if (dmi_check_system(intel_no_lvds)) {
+		WARN(!dev_priv->vbt.int_lvds_support,
+		     "Useless DMI match. Internal LVDS support disabled by VBT\n");
 		return;
+	}
 
 	if (!dev_priv->vbt.int_lvds_support) {
 		DRM_DEBUG_KMS("Internal LVDS support disabled by VBT\n");
diff --git a/drivers/gpu/drm/i915/intel_vbt_defs.h b/drivers/gpu/drm/i915/intel_vbt_defs.h
index 458468237b5f..39c804624179 100644
--- a/drivers/gpu/drm/i915/intel_vbt_defs.h
+++ b/drivers/gpu/drm/i915/intel_vbt_defs.h
@@ -635,7 +635,7 @@ struct bdb_sdvo_lvds_options {
 #define BDB_DRIVER_FEATURE_NO_LVDS		0
 #define BDB_DRIVER_FEATURE_INT_LVDS		1
 #define BDB_DRIVER_FEATURE_SDVO_LVDS		2
-#define BDB_DRIVER_FEATURE_EDP			3
+#define BDB_DRIVER_FEATURE_INT_SDVO_LVDS	3
 
 struct bdb_driver_features {
 	u8 boot_dev_algorithm:1;
-- 
2.16.1

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