drm/i915: Short-circuit no-op vga_set_state()

Touching the VGA registers risks a hard machine hang, at least on this
ivb machine after removing a conflicting efifb. This is more than likely
related to the discovery that VGA IO decode on the more recent PCH
platforms is terminally broken.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index cc426e10d746b3e611a7dfa69ec8429d99bf9c99..1b2faa44764b164d1b6ce00aff3e0630168190da 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -11513,6 +11513,9 @@ int intel_modeset_vga_set_state(struct drm_device *dev, bool state)
                return -EIO;
        }
 
+       if (!!(gmch_ctrl & INTEL_GMCH_VGA_DISABLE) == !state)
+               return 0;
+
        if (state)
                gmch_ctrl &= ~INTEL_GMCH_VGA_DISABLE;
        else