drm/i915/skl: Restore pipe interrupt registers after power well enabling

The pipe interrupt registers are in the actual pipe power well, so we
need to restore them when re-enable the corresponding power well.

I've also copied what we do on HSW/BDW for VGA, even if the we haven't
enabled unclaimed registers just yet.

v2: Don't run skl_power_well_post_enable() if the power well is already
    enabled (Paulo)
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -3175,6 +3175,10 @@ void gen8_irq_power_well_post_enable(struct drm_i915_private *dev_priv,
 	uint32_t extra_ier = GEN8_PIPE_VBLANK | GEN8_PIPE_FIFO_UNDERRUN;
 
 	spin_lock_irq(&dev_priv->irq_lock);
+	if (pipe_mask & 1 << PIPE_A)
+		GEN8_IRQ_INIT_NDX(DE_PIPE, PIPE_A,
+				  dev_priv->de_irq_mask[PIPE_A],
+				  ~dev_priv->de_irq_mask[PIPE_A] | extra_ier);
 	if (pipe_mask & 1 << PIPE_B)
 		GEN8_IRQ_INIT_NDX(DE_PIPE, PIPE_B,
 				  dev_priv->de_irq_mask[PIPE_B],

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -199,6 +199,34 @@ static void hsw_power_well_post_enable(struct drm_i915_private *dev_priv)
 						1 << PIPE_C | 1 << PIPE_B);
 }
 
+static void skl_power_well_post_enable(struct drm_i915_private *dev_priv,
+				       struct i915_power_well *power_well)
+{
+	struct drm_device *dev = dev_priv->dev;
+
+	/*
+	 * After we re-enable the power well, if we touch VGA register 0x3d5
+	 * we'll get unclaimed register interrupts. This stops after we write
+	 * anything to the VGA MSR register. The vgacon module uses this
+	 * register all the time, so if we unbind our driver and, as a
+	 * consequence, bind vgacon, we'll get stuck in an infinite loop at
+	 * console_unlock(). So make here we touch the VGA MSR register, making
+	 * sure vgacon can keep working normally without triggering interrupts
+	 * and error messages.
+	 */
+	if (power_well->data == SKL_DISP_PW_2) {
+		vga_get_uninterruptible(dev->pdev, VGA_RSRC_LEGACY_IO);
+		outb(inb(VGA_MSR_READ), VGA_MSR_WRITE);
+		vga_put(dev->pdev, VGA_RSRC_LEGACY_IO);
+
+		gen8_irq_power_well_post_enable(dev_priv,
+						1 << PIPE_C | 1 << PIPE_B);
+	}
+
+	if (power_well->data == SKL_DISP_PW_1)
+		gen8_irq_power_well_post_enable(dev_priv, 1 << PIPE_A);
+}
+
 static void hsw_set_power_well(struct drm_i915_private *dev_priv,
 			       struct i915_power_well *power_well, bool enable)
 {
@@ -361,6 +389,9 @@ static void skl_set_power_well(struct drm_i915_private *dev_priv,
 				DRM_ERROR("PG2 distributing status timeout\n");
 		}
 	}
+
+	if (enable && !is_enabled)
+		skl_power_well_post_enable(dev_priv, power_well);
 }
 
 static void hsw_power_well_sync_hw(struct drm_i915_private *dev_priv,