gma500: panel presence check

Introduce a panel presence check for Cedartrail. Non netbook devices don't
necessarily have a panel attached.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/drivers/gpu/drm/gma500/cdv_intel_lvds.c b/drivers/gpu/drm/gma500/cdv_intel_lvds.c
index 8359c1a3f45f..c87b179eadfd 100644
--- a/drivers/gpu/drm/gma500/cdv_intel_lvds.c
+++ b/drivers/gpu/drm/gma500/cdv_intel_lvds.c
@@ -556,6 +556,56 @@ const struct drm_encoder_funcs cdv_intel_lvds_enc_funcs = {
         .destroy = cdv_intel_lvds_enc_destroy,
 };
 
+/*
+ * Enumerate the child dev array parsed from VBT to check whether
+ * the LVDS is present.
+ * If it is present, return 1.
+ * If it is not present, return false.
+ * If no child dev is parsed from VBT, it assumes that the LVDS is present.
+ */
+static bool lvds_is_present_in_vbt(struct drm_device *dev,
+                                   u8 *i2c_pin)
+{
+        struct drm_psb_private *dev_priv = dev->dev_private;
+        int i;
+
+        if (!dev_priv->child_dev_num)
+                return true;
+
+        for (i = 0; i < dev_priv->child_dev_num; i++) {
+                struct child_device_config *child = dev_priv->child_dev + i;
+
+                /* If the device type is not LFP, continue.
+                 * We have to check both the new identifiers as well as the
+                 * old for compatibility with some BIOSes.
+                 */
+                if (child->device_type != DEVICE_TYPE_INT_LFP &&
+                    child->device_type != DEVICE_TYPE_LFP)
+                        continue;
+
+                if (child->i2c_pin)
+                    *i2c_pin = child->i2c_pin;
+
+                /* However, we cannot trust the BIOS writers to populate
+                 * the VBT correctly.  Since LVDS requires additional
+                 * information from AIM blocks, a non-zero addin offset is
+                 * a good indicator that the LVDS is actually present.
+                 */
+                if (child->addin_offset)
+                        return true;
+
+                /* But even then some BIOS writers perform some black magic
+                 * and instantiate the device without reference to any
+                 * additional data.  Trust that if the VBT was written into
+                 * the OpRegion then they have validated the LVDS's existence.
+                 */
+                if (dev_priv->opregion.vbt)
+                        return true;
+        }
+
+        return false;
+}
+
 /**
  * cdv_intel_lvds_init - setup LVDS connectors on this device
  * @dev: drm device
@@ -576,6 +626,13 @@ void cdv_intel_lvds_init(struct drm_device *dev,
         struct drm_psb_private *dev_priv = dev->dev_private;
         u32 lvds;
         int pipe;
+        u8 pin;
+
+        pin = GMBUS_PORT_PANEL;
+        if (!lvds_is_present_in_vbt(dev, &pin)) {
+                DRM_DEBUG_KMS("LVDS is not present in VBT\n");
+                return;
+        }
 
         psb_intel_encoder = kzalloc(sizeof(struct psb_intel_encoder),
                                     GFP_KERNEL);