drm/i915/crt: Use a DDC probe on 0xA0 before load-detect

The BIOS writer's guide suggests that a VGA connection will ACK a write
to address 0xA0 and that this should be used before doing legacy
load-detection. Considering the extreme cost of load-detection,
performing an extra DDC seems a risk worth taking.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 35 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 8e484c9ac1f5..389fcd2aea1f 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -261,6 +261,21 @@ static bool intel_crt_detect_hotplug(struct drm_connector *connector)
         return ret;
 }
 
+static bool intel_crt_ddc_probe(struct drm_i915_private *dev_priv, int ddc_bus)
+{
+        u8 buf;
+        struct i2c_msg msgs[] = {
+                {
+                        .addr = 0xA0,
+                        .flags = 0,
+                        .len = 1,
+                        .buf = &buf,
+                },
+        };
+        /* DDC monitor detect: Does it ACK a write to 0xA0? */
+        return i2c_transfer(&dev_priv->gmbus[ddc_bus].adapter, msgs, 1) == 1;
+}
+
 static bool intel_crt_detect_ddc(struct drm_encoder *encoder)
 {
         struct intel_encoder *intel_encoder = to_intel_encoder(encoder);
@@ -270,7 +285,17 @@ static bool intel_crt_detect_ddc(struct drm_encoder *encoder)
         if (intel_encoder->type != INTEL_OUTPUT_ANALOG)
                 return false;
 
-        return intel_ddc_probe(intel_encoder, dev_priv->crt_ddc_pin);
+        if (intel_crt_ddc_probe(dev_priv, dev_priv->crt_ddc_pin)) {
+                DRM_DEBUG_KMS("CRT detected via DDC:0xa0\n");
+                return true;
+        }
+
+        if (intel_ddc_probe(intel_encoder, dev_priv->crt_ddc_pin)) {
+                DRM_DEBUG_KMS("CRT detected via DDC:0x50 [EDID]\n");
+                return true;
+        }
+
+        return false;
 }
 
 static enum drm_connector_status
@@ -296,6 +321,8 @@ intel_crt_load_detect(struct drm_crtc *crtc, struct intel_encoder *intel_encoder
         uint8_t st00;
         enum drm_connector_status status;
 
+        DRM_DEBUG_KMS("starting load-detect on CRT\n");
+
         if (pipe == 0) {
                 bclrpat_reg = BCLRPAT_A;
                 vtotal_reg = VTOTAL_A;
@@ -412,9 +439,10 @@ intel_crt_detect(struct drm_connector *connector, bool force)
         enum drm_connector_status status;
 
         if (I915_HAS_HOTPLUG(dev)) {
-                if (intel_crt_detect_hotplug(connector))
+                if (intel_crt_detect_hotplug(connector)) {
+                        DRM_DEBUG_KMS("CRT detected via hotplug\n");
                         return connector_status_connected;
-                else
+                } else
                         return connector_status_disconnected;
         }
 
@@ -431,7 +459,10 @@ intel_crt_detect(struct drm_connector *connector, bool force)
                 crtc = intel_get_load_detect_pipe(encoder, connector,
                                                   NULL, &dpms_mode);
                 if (crtc) {
-                        status = intel_crt_load_detect(crtc, encoder);
+                        if (intel_crt_detect_ddc(&encoder->base))
+                                status = connector_status_connected;
+                        else
+                                status = intel_crt_load_detect(crtc, encoder);
                         intel_release_load_detect_pipe(encoder,
                                                        connector, dpms_mode);
                 } else