drm/i915: don't allow interlaced pipeconf on gen2

gen2 doesn't support it, so be a bit more paranoid and add a check to
ensure that we never ever set an unsupported interlaced bit.

Ensure that userspace can't set an interlaced mode by resetting
interlace_allowed for the crt on gen2. dvo and lvds are the only other
encoders that gen2 supports and these already disallow interlaced
modes.
Reviewed-by: NEugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-Off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_crt.c

@@ -594,7 +594,10 @@ void intel_crt_init(struct drm_device *dev)
 				1 << INTEL_ANALOG_CLONE_BIT |
 				1 << INTEL_SDVO_LVDS_CLONE_BIT);
 	crt->base.crtc_mask = (1 << 0) | (1 << 1);
-	connector->interlace_allowed = 1;
+	if (IS_GEN2(dev))
+		connector->interlace_allowed = 0;
+	else
+		connector->interlace_allowed = 1;
 	connector->doublescan_allowed = 0;
 
 	drm_encoder_helper_add(&crt->base.base, &intel_crt_helper_funcs);

drivers/gpu/drm/i915/intel_display.c

@@ -5385,7 +5385,8 @@ static int i9xx_crtc_mode_set(struct drm_crtc *crtc,
 	}
 
 	pipeconf &= ~PIPECONF_INTERLACE_MASK;
-	if (adjusted_mode->flags & DRM_MODE_FLAG_INTERLACE) {
+	if (!IS_GEN2(dev) &&
+	    adjusted_mode->flags & DRM_MODE_FLAG_INTERLACE) {
 		pipeconf |= PIPECONF_INTERLACE_W_FIELD_INDICATION;
 		/* the chip adds 2 halflines automatically */
 		adjusted_mode->crtc_vtotal -= 1;