drm/i915: Fix IPS related flicker

We cannot let IPS enabled with no plane on the pipe:

BSpec: "IPS cannot be enabled until after at least one plane has
been enabled for at least one vertical blank." and "IPS must be
disabled while there is still at least one plane enabled on the
same pipe as IPS." This restriction apply to HSW and BDW.

However a shortcut path on update primary plane function
to make primary plane invisible by setting DSPCTRL to 0
was leting IPS enabled while there was no
other plane enabled on the pipe causing flickerings that we were
believing that it was caused by that other restriction where
ips cannot be used when pixel rate is greater than 95% of cdclok.

v2: Don't mess with Atomic path as pointed out by Ville.

Reference: https://bugs.freedesktop.org/show_bug.cgi?id=85583
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -13303,6 +13303,16 @@ intel_check_primary_plane(struct drm_plane *plane,
 				intel_crtc->atomic.wait_vblank = true;
 		}
 
+		/*
+		 * FIXME: Actually if we will still have any other plane enabled
+		 * on the pipe we could let IPS enabled still, but for
+		 * now lets consider that when we make primary invisible
+		 * by setting DSPCNTR to 0 on update_primary_plane function
+		 * IPS needs to be disable.
+		 */
+		if (!state->visible || !fb)
+			intel_crtc->atomic.disable_ips = true;
+
 		intel_crtc->atomic.fb_bits |=
 			INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe);
 
@@ -13400,6 +13410,9 @@ static void intel_begin_crtc_commit(struct drm_crtc *crtc)
 	if (intel_crtc->atomic.disable_fbc)
 		intel_fbc_disable(dev);
 
+	if (intel_crtc->atomic.disable_ips)
+		hsw_disable_ips(intel_crtc);
+
 	if (intel_crtc->atomic.pre_disable_primary)
 		intel_pre_disable_primary(crtc);
 

drivers/gpu/drm/i915/intel_drv.h

@@ -485,6 +485,7 @@ struct intel_crtc_atomic_commit {
 	/* Sleepable operations to perform before commit */
 	bool wait_for_flips;
 	bool disable_fbc;
+	bool disable_ips;
 	bool pre_disable_primary;
 	bool update_wm;
 	unsigned disabled_planes;