drm/i915: fix gpio register detection logic for BIOS without VBT

if no VBT is present, crt_ddc_bus will be left at 0, and cause us
to use that for the GPIO register offset. That's never a valid register
offset, so let the "undefined" value be 0 instead of -1.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
[anholt: clarified the commit message a bit]

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 0864a2c4085..477a61c5402 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -526,7 +526,7 @@ void intel_crt_init(struct drm_device *dev)
         else {
                 i2c_reg = GPIOA;
                 /* Use VBT information for CRT DDC if available */
-                if (dev_priv->crt_ddc_bus != -1)
+                if (dev_priv->crt_ddc_bus != 0)
                         i2c_reg = dev_priv->crt_ddc_bus;
         }
         intel_output->ddc_bus = intel_i2c_create(dev, i2c_reg, "CRTDDC_A");