drm/i915: Take advantage of auto-polling CRT hotplug detection on PCH hardware

Both IBX and CPT have an automatic hotplug detection mode which appears to work reliably enough
that we can dispense with the manual force hotplug trigger stuff. This means that
hotplug detection is as simple as reading the current hotplug register values.

The first time the hotplug detection is activated, the code synchronously waits for a hotplug
sequence in case the hardware hasn't bothered to do a detection cycle since being initialized.

Signed-off-by: Keith Packard <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>

drivers/gpu/drm/i915/intel_crt.c

···
 #include "i915_drm.h"
 #include "i915_drv.h"
 
+/* Here's the desired hotplug mode */
+#define ADPA_HOTPLUG_BITS (ADPA_CRT_HOTPLUG_PERIOD_128 |		\
+			   ADPA_CRT_HOTPLUG_WARMUP_10MS |		\
+			   ADPA_CRT_HOTPLUG_SAMPLE_4S |			\
+			   ADPA_CRT_HOTPLUG_VOLTAGE_50 |		\
+			   ADPA_CRT_HOTPLUG_VOLREF_325MV |		\
+			   ADPA_CRT_HOTPLUG_ENABLE)
+
 struct intel_crt {
 	struct intel_encoder base;
+	bool force_hotplug_required;
 };
 
 static struct intel_crt *intel_attached_crt(struct drm_connector *connector)
···
 			   dpll_md & ~DPLL_MD_UDI_MULTIPLIER_MASK);
 	}
 
-	adpa = 0;
+	adpa = ADPA_HOTPLUG_BITS;
 	if (adjusted_mode->flags & DRM_MODE_FLAG_PHSYNC)
 		adpa |= ADPA_HSYNC_ACTIVE_HIGH;
 	if (adjusted_mode->flags & DRM_MODE_FLAG_PVSYNC)
···
 static bool intel_ironlake_crt_detect_hotplug(struct drm_connector *connector)
 {
 	struct drm_device *dev = connector->dev;
+	struct intel_crt *crt = intel_attached_crt(connector);
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	u32 adpa, temp;
+	u32 adpa;
 	bool ret;
-	bool turn_off_dac = false;
 
-	temp = adpa = I915_READ(PCH_ADPA);
+	/* The first time through, trigger an explicit detection cycle */
+	if (crt->force_hotplug_required) {
+		bool turn_off_dac = HAS_PCH_SPLIT(dev);
+		u32 save_adpa;
 
-	if (HAS_PCH_SPLIT(dev))
-		turn_off_dac = true;
+		crt->force_hotplug_required = 0;
 
-	adpa &= ~ADPA_CRT_HOTPLUG_MASK;
-	if (turn_off_dac)
-		adpa &= ~ADPA_DAC_ENABLE;
+		save_adpa = adpa = I915_READ(PCH_ADPA);
+		DRM_DEBUG_KMS("trigger hotplug detect cycle: adpa=0x%x\n", adpa);
 
-	/* disable HPD first */
-	I915_WRITE(PCH_ADPA, adpa);
-	(void)I915_READ(PCH_ADPA);
+		adpa |= ADPA_CRT_HOTPLUG_FORCE_TRIGGER;
+		if (turn_off_dac)
+			adpa &= ~ADPA_DAC_ENABLE;
 
-	adpa |= (ADPA_CRT_HOTPLUG_PERIOD_128 |
-			ADPA_CRT_HOTPLUG_WARMUP_10MS |
-			ADPA_CRT_HOTPLUG_SAMPLE_4S |
-			ADPA_CRT_HOTPLUG_VOLTAGE_50 | /* default */
-			ADPA_CRT_HOTPLUG_VOLREF_325MV |
-			ADPA_CRT_HOTPLUG_ENABLE |
-			ADPA_CRT_HOTPLUG_FORCE_TRIGGER);
+		I915_WRITE(PCH_ADPA, adpa);
 
-	DRM_DEBUG_KMS("pch crt adpa 0x%x", adpa);
-	I915_WRITE(PCH_ADPA, adpa);
+		if (wait_for((I915_READ(PCH_ADPA) & ADPA_CRT_HOTPLUG_FORCE_TRIGGER) == 0,
+			     1000))
+			DRM_DEBUG_KMS("timed out waiting for FORCE_TRIGGER");
 
-	if (wait_for((I915_READ(PCH_ADPA) & ADPA_CRT_HOTPLUG_FORCE_TRIGGER) == 0,
-		     1000))
-		DRM_DEBUG_KMS("timed out waiting for FORCE_TRIGGER");
-
-	if (turn_off_dac) {
-		/* Make sure hotplug is enabled */
-		I915_WRITE(PCH_ADPA, temp | ADPA_CRT_HOTPLUG_ENABLE);
-		(void)I915_READ(PCH_ADPA);
+		if (turn_off_dac) {
+			I915_WRITE(PCH_ADPA, save_adpa);
+			POSTING_READ(PCH_ADPA);
+		}
 	}
 
 	/* Check the status to see if both blue and green are on now */
 	adpa = I915_READ(PCH_ADPA);
-	adpa &= ADPA_CRT_HOTPLUG_MONITOR_MASK;
-	if ((adpa == ADPA_CRT_HOTPLUG_MONITOR_COLOR) ||
-		(adpa == ADPA_CRT_HOTPLUG_MONITOR_MONO))
+	if ((adpa & ADPA_CRT_HOTPLUG_MONITOR_MASK) != 0)
 		ret = true;
 	else
 		ret = false;
+	DRM_DEBUG_KMS("ironlake hotplug adpa=0x%x, result %d\n", adpa, ret);
 
 	return ret;
 }
···
 		if (intel_crt_detect_hotplug(connector)) {
 			DRM_DEBUG_KMS("CRT detected via hotplug\n");
 			return connector_status_connected;
-		} else
+		} else {
+			DRM_DEBUG_KMS("CRT not detected via hotplug\n");
 			return connector_status_disconnected;
+		}
 	}
 
 	if (intel_crt_detect_ddc(crt))
···
 		connector->polled = DRM_CONNECTOR_POLL_HPD;
 	else
 		connector->polled = DRM_CONNECTOR_POLL_CONNECT;
+
+	/*
+	 * Configure the automatic hotplug detection stuff
+	 */
+	crt->force_hotplug_required = 0;
+	if (HAS_PCH_SPLIT(dev)) {
+		u32 adpa;
+
+		adpa = I915_READ(PCH_ADPA);
+		adpa &= ~ADPA_CRT_HOTPLUG_MASK;
+		adpa |= ADPA_HOTPLUG_BITS;
+		I915_WRITE(PCH_ADPA, adpa);
+		POSTING_READ(PCH_ADPA);
+
+		DRM_DEBUG_KMS("pch crt adpa set to 0x%x\n", adpa);
+		crt->force_hotplug_required = 1;
+	}
 
 	dev_priv->hotplug_supported_mask |= CRT_HOTPLUG_INT_STATUS;
 }