drm/i915: Check for FIFO underruns at the end of modeset on gmch

FIFO underruns don't generate interrupts on gmch platforms, so
if we want to know whether a modeset triggered FIFO underruns we
need to explicitly check for them.

As a modeset on one pipe could cause underruns on other pipes,
check for underruns on all pipes.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Thomas Wood <thomas.wood@intel.com>
[danvet: Fix up merge error, kudos to Ville for noticing it.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -306,6 +306,34 @@ static bool cpt_can_enable_serr_int(struct drm_device *dev)
 	return true;
 }
 
+void i9xx_check_fifo_underruns(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct intel_crtc *crtc;
+	unsigned long flags;
+
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
+
+	for_each_intel_crtc(dev, crtc) {
+		u32 reg = PIPESTAT(crtc->pipe);
+		u32 pipestat;
+
+		if (crtc->cpu_fifo_underrun_disabled)
+			continue;
+
+		pipestat = I915_READ(reg) & 0xffff0000;
+		if ((pipestat & PIPE_FIFO_UNDERRUN_STATUS) == 0)
+			continue;
+
+		I915_WRITE(reg, pipestat | PIPE_FIFO_UNDERRUN_STATUS);
+		POSTING_READ(reg);
+
+		DRM_ERROR("pipe %c underrun\n", pipe_name(crtc->pipe));
+	}
+
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+}
+
 static void i9xx_set_fifo_underrun_reporting(struct drm_device *dev,
 					     enum pipe pipe, bool enable)
 {

drivers/gpu/drm/i915/intel_display.c

@@ -4625,6 +4625,9 @@ static void valleyview_crtc_enable(struct drm_crtc *crtc)
 	intel_crtc_enable_planes(crtc);
 
 	drm_crtc_vblank_on(crtc);
+
+	/* Underruns don't raise interrupts, so check manually. */
+	i9xx_check_fifo_underruns(dev);
 }
 
 static void i9xx_set_pll_dividers(struct intel_crtc *crtc)
@@ -4704,6 +4707,9 @@ static void i9xx_crtc_enable(struct drm_crtc *crtc)
 	intel_crtc_enable_planes(crtc);
 
 	drm_crtc_vblank_on(crtc);
+
+	/* Underruns don't raise interrupts, so check manually. */
+	i9xx_check_fifo_underruns(dev);
 }
 
 static void i9xx_pfit_disable(struct intel_crtc *crtc)

drivers/gpu/drm/i915/intel_drv.h

@@ -680,6 +680,7 @@ void bdw_disable_pm_irq(struct drm_i915_private *dev_priv, uint32_t mask);
 void intel_runtime_pm_disable_interrupts(struct drm_device *dev);
 void intel_runtime_pm_restore_interrupts(struct drm_device *dev);
 int intel_get_crtc_scanline(struct intel_crtc *crtc);
+void i9xx_check_fifo_underruns(struct drm_device *dev);
 
 
 /* intel_crt.c */