[PATCH v2 2/2] drm/i915/vlv: Reset the ADPA in vlv_display_power_well_init()

[Lyude]

While VGA hotplugging worked(ish) before, it looks like that was mainly
because we'd unintentionally enable it in
valleyview_crt_detect_hotplug() when we did a force trigger. This
doesn't work reliably enough because whenever the display powerwell on
vlv gets disabled, the values set in VLV_ADPA get cleared and
consequently VGA hotplugging gets disabled. This causes bugs such as one
we found on an Intel NUC, where doing the following sequence of
hotplugs:

      - Disconnect all monitors
      - Connect VGA
      - Disconnect VGA
      - Connect HDMI

Would result in VGA hotplugging becoming disabled, due to the powerwells
getting toggled in the process of connecting HDMI.

Changes since v1:
 - Instead of handling the register writes ourself, we just reuse
   intel_crt_detect()
 - Instead of resetting the ADPA during display IRQ installation, we now
   reset them in vlv_display_power_well_init()

CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
---
 drivers/gpu/drm/i915/intel_runtime_pm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
index 80e8bd4..c7d195f 100644
--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -902,6 +902,7 @@ static bool vlv_power_well_enabled(struct drm_i915_private *dev_priv,
 
 static void vlv_display_power_well_init(struct drm_i915_private *dev_priv)
 {
+	struct drm_encoder *encoder, *vga_encoder = NULL;
 	enum pipe pipe;
 
 	/*
@@ -935,6 +936,17 @@ static void vlv_display_power_well_init(struct drm_i915_private *dev_priv)
 
 	intel_hpd_init(dev_priv);
 
+	/* Re-enable the ADPA, if we have one */
+	drm_for_each_encoder(encoder, dev_priv->dev) {
+		if (encoder->encoder_type == DRM_MODE_ENCODER_DAC) {
+			vga_encoder = encoder;
+			break;
+		}
+	}
+
+	if (vga_encoder && vga_encoder->funcs->reset)
+		vga_encoder->funcs->reset(vga_encoder);
+
 	i915_redisable_vga_power_on(dev_priv->dev);
 }
 
-- 
2.5.5