drm/i915: Track pfit enable state separately from size

Detangle the additional state of whether or not the hw has the pfit
enabled from whether it has zero size. This allows us to cleanly
distinguish in the code when we expect the pfit to be enabled (for
Haswell pc8), and when the BIOS is confused and needs sanitizing.

Reported-by: shui yanwei <yangweix.shui@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68251
Tested-by: shui yanwei <yangweix.shui@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 0c115cc..dd176b7 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2096,16 +2096,16 @@
 				    struct drm_crtc *crtc)
 {
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
-	uint32_t pixel_rate, pfit_size;
+	uint32_t pixel_rate;
 
 	pixel_rate = intel_crtc->config.adjusted_mode.clock;
 
 	/* We only use IF-ID interlacing. If we ever use PF-ID we'll need to
 	 * adjust the pixel_rate here. */
 
-	pfit_size = intel_crtc->config.pch_pfit.size;
-	if (pfit_size) {
+	if (intel_crtc->config.pch_pfit.enabled) {
 		uint64_t pipe_w, pipe_h, pfit_w, pfit_h;
+		uint32_t pfit_size = intel_crtc->config.pch_pfit.size;
 
 		pipe_w = intel_crtc->config.requested_mode.hdisplay;
 		pipe_h = intel_crtc->config.requested_mode.vdisplay;