[Intel-gfx] [PATCH] drm/i915: Document IPS restriction with 1 plane on the pipe.

[Rodrigo Vivi]

With this well documented we can remove that FIXME comment.

We just need to make sure that on primary -> sprite transition there
is no vblank time where ips gets alone on the pipe with absolutelly
no plane. If this happens even for a quickly momment IPS won't get
recovered and it might cause strange flickering screens.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 37 ++++++++++++++++++++++++------------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 5519d56..d2c417b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -4620,6 +4620,17 @@ static void intel_enable_sprite_planes(struct drm_crtc *crtc)
 	}
 }
 
+/**
+ * hsw_enable_ips - Enable IPS
+ * @intel_crtc: crtc
+ *
+ * This function needs to be called after there are at least on plane enabled
+ * on the pipe.
+ *
+ * IPS is fine as long as one plane is enabled.
+ *
+ * Pre-requisite: IPS cannot be enabled until after at least one plane has been enabled for at least one vertical blank.
+ */
 void hsw_enable_ips(struct intel_crtc *crtc)
 {
 	struct drm_device *dev = crtc->base.dev;
@@ -4653,6 +4664,20 @@ void hsw_enable_ips(struct intel_crtc *crtc)
 	}
 }
 
+/**
+ * hsw_disable_ips - Disable IPS
+ * @intel_crtc: crtc
+ *
+ * This function needs to be called everytime that there will be no plane
+ * enabled on the pipe on the next vblank.
+ *
+ * IPS is fine as long as one plane is enabled, however it gets confused
+ * in a non recoverable state when it stays enabled on the pipe with no
+ * other plane enabled at same vblank time. So please make sure this
+ * function is called everytime that we have no plane enabled on the pipe.
+ *
+ * Pre-requisite: IPS must be disabled while there is still at least one plane enabled on the same pipe as IPS.
+ */
 void hsw_disable_ips(struct intel_crtc *crtc)
 {
 	struct drm_device *dev = crtc->base.dev;
@@ -4769,12 +4794,6 @@ intel_post_enable_primary(struct drm_crtc *crtc)
 	if (IS_BROADWELL(dev))
 		intel_wait_for_vblank(dev, pipe);
 
-	/*
-	 * FIXME IPS should be fine as long as one plane is
-	 * enabled, but in practice it seems to have problems
-	 * when going from primary only to sprite only and vice
-	 * versa.
-	 */
 	hsw_enable_ips(intel_crtc);
 
 	mutex_lock(&dev->struct_mutex);
@@ -4840,12 +4859,6 @@ intel_pre_disable_primary(struct drm_crtc *crtc)
 		intel_fbc_disable(dev);
 	mutex_unlock(&dev->struct_mutex);
 
-	/*
-	 * FIXME IPS should be fine as long as one plane is
-	 * enabled, but in practice it seems to have problems
-	 * when going from primary only to sprite only and vice
-	 * versa.
-	 */
 	hsw_disable_ips(intel_crtc);
 }
 
-- 
2.1.0