drm/i915: disable hotplug detect before Ironlake CRT detect

commit eceb784cec4dc0fcc2993d9ee4a7c0d111ada80a upstream.

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.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 6d3730f327cf6365a39d780d1e26cc040aeea77b..5e730e6f8a74942bd5afb20dd24affac9fdd7359 100644 (file)
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -185,6 +185,9 @@ static bool intel_igdng_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 |