[PATCH] drm/i915: don't try and probe dpcd if we have no dp configured

[Dave Airlie <airlied@gmail.com>]

On hsw/bdw VBT can signal no DP on a digital connector, so when we
get a hotplug irq in that situation, don't continue if we haven't
actually got a DP output register configured.

This fixes an oops where the aux mutex isn't initialised.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81856
Reported-by: lei.a.liu@intel.com
Signed-off-by: Dave Airlie <airlied@redhat.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index e7a7953..691d169 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3966,6 +3966,9 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
 		if (!ibx_digital_port_connected(dev_priv, intel_dig_port))
 			goto mst_fail;
 
+		if (!intel_dp->output_reg)
+			goto mst_fail;
+
 		if (!intel_dp_get_dpcd(intel_dp)) {
 			goto mst_fail;
 		}
-- 
1.9.3