drm/i915: disable hotplug detect before Ironlake CRT detect

This tries to fix CRT detect loop hang seen on some Ironlake form
factor, to clear up hotplug detect state before taking CRT detect
to make sure next hotplug detect cycle is consistent.

Cc: Stable Team <stable@kernel.org>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index ddefc871edfe4806714a07d44444f1e08e5422af..79dd4026586fa55f6072b05bb27a9fce2734099a 100644 (file)
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -157,6 +157,9 @@ static bool intel_ironlake_crt_detect_hotplug(struct drm_connector *connector)
        adpa = I915_READ(PCH_ADPA);
 
        adpa &= ~ADPA_CRT_HOTPLUG_MASK;
+       /* disable HPD first */
+       I915_WRITE(PCH_ADPA, adpa);
+       (void)I915_READ(PCH_ADPA);
 
        adpa |= (ADPA_CRT_HOTPLUG_PERIOD_128 |
                        ADPA_CRT_HOTPLUG_WARMUP_10MS |