drm/i915: disable shared panel fitter for pipe

If encoder is switched off by BIOS, but the panel fitter is left on,
we never try to turn off the panel fitter and leave it still attached
to the pipe - which can cause blurry output elsewhere.

Based on work by Chris Wilson <chris@chris-wilson.co.uk>

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=58867
Cc: stable@vger.kernel.org
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Tested-by: Andreas Sturmlechner <andreas.sturmlechner@gmail.com>
[danvet: Remove the redundant HAS_PCH_SPLIT check and add a tiny
comment.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -3637,6 +3637,7 @@ static void i9xx_crtc_disable(struct drm_crtc *crtc)
 	struct intel_encoder *encoder;
 	int pipe = intel_crtc->pipe;
 	int plane = intel_crtc->plane;
+	u32 pctl;
 
 
 	if (!intel_crtc->active)
@@ -3656,6 +3657,13 @@ static void i9xx_crtc_disable(struct drm_crtc *crtc)
 
 	intel_disable_plane(dev_priv, plane, pipe);
 	intel_disable_pipe(dev_priv, pipe);
+
+	/* Disable pannel fitter if it is on this pipe. */
+	pctl = I915_READ(PFIT_CONTROL);
+	if ((pctl & PFIT_ENABLE) &&
+	    ((pctl & PFIT_PIPE_MASK) >> PFIT_PIPE_SHIFT) == pipe)
+		I915_WRITE(PFIT_CONTROL, 0);
+
 	intel_disable_pll(dev_priv, pipe);
 
 	intel_crtc->active = false;