drm/i915: Don't lock panel registers when downclocking

This patch replaces the locking from the downclock routines with an assert
to ensure the registers are indeed unlocked. Without this patch, pre-SNB
devices would lock the registers when downclocking which would cause a
WARNING on suspend/resume with downclocking enabled.

Note: To hit this bug, you need to have lvds downclocking enabled.
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -7006,9 +7006,7 @@ static void intel_increase_pllclock(struct drm_crtc *crtc)
 	if (!HAS_PIPE_CXSR(dev) && (dpll & DISPLAY_RATE_SELECT_FPA1)) {
 		DRM_DEBUG_DRIVER("upclocking LVDS\n");
 
-		/* Unlock panel regs */
-		I915_WRITE(PP_CONTROL,
-			   I915_READ(PP_CONTROL) | PANEL_UNLOCK_REGS);
+		assert_panel_unlocked(dev_priv, pipe);
 
 		dpll &= ~DISPLAY_RATE_SELECT_FPA1;
 		I915_WRITE(dpll_reg, dpll);
@@ -7017,9 +7015,6 @@ static void intel_increase_pllclock(struct drm_crtc *crtc)
 		dpll = I915_READ(dpll_reg);
 		if (dpll & DISPLAY_RATE_SELECT_FPA1)
 			DRM_DEBUG_DRIVER("failed to upclock LVDS!\n");
-
-		/* ...and lock them again */
-		I915_WRITE(PP_CONTROL, I915_READ(PP_CONTROL) & 0x3);
 	}
 
 	/* Schedule downclock */
@@ -7049,9 +7044,7 @@ static void intel_decrease_pllclock(struct drm_crtc *crtc)
 	if (!HAS_PIPE_CXSR(dev) && intel_crtc->lowfreq_avail) {
 		DRM_DEBUG_DRIVER("downclocking LVDS\n");
 
-		/* Unlock panel regs */
-		I915_WRITE(PP_CONTROL, I915_READ(PP_CONTROL) |
-			   PANEL_UNLOCK_REGS);
+		assert_panel_unlocked(dev_priv, pipe);
 
 		dpll |= DISPLAY_RATE_SELECT_FPA1;
 		I915_WRITE(dpll_reg, dpll);
@@ -7059,9 +7052,6 @@ static void intel_decrease_pllclock(struct drm_crtc *crtc)
 		dpll = I915_READ(dpll_reg);
 		if (!(dpll & DISPLAY_RATE_SELECT_FPA1))
 			DRM_DEBUG_DRIVER("failed to downclock LVDS!\n");
-
-		/* ...and lock them again */
-		I915_WRITE(PP_CONTROL, I915_READ(PP_CONTROL) & 0x3);
 	}
 
 }