drm/i915: program WM_LINETIME on Haswell

The line time can be programmed according to the number of horizontal
pixels vs effective pixel rate ratio.

v2: improve comment as per Chris Wilson suggestion

v3: incorporate latest changes in specs.

v4: move into wm update routine, also mention that the same routine can
program IPS watermarks. We do not have their enablement code yet, nor
handle the required clock settings at the moment, so this patch won't
program those values for now.

Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -243,6 +243,8 @@ struct drm_i915_display_funcs {
 	void (*update_sprite_wm)(struct drm_device *dev, int pipe,
 				 uint32_t sprite_width, int pixel_size);
 	void (*sanitize_pm)(struct drm_device *dev);
+	void (*update_linetime_wm)(struct drm_device *dev, int pipe,
+				 struct drm_display_mode *mode);
 	int (*crtc_mode_set)(struct drm_crtc *crtc,
 			     struct drm_display_mode *mode,
 			     struct drm_display_mode *adjusted_mode,

drivers/gpu/drm/i915/intel_display.c

@@ -4609,6 +4609,8 @@ static int ironlake_crtc_mode_set(struct drm_crtc *crtc,
 
 	intel_update_watermarks(dev);
 
+	intel_update_linetime_watermarks(dev, pipe, adjusted_mode);
+
 	return ret;
 }
 

drivers/gpu/drm/i915/intel_drv.h

@@ -454,6 +454,8 @@ extern void intel_update_watermarks(struct drm_device *dev);
 extern void intel_update_sprite_watermarks(struct drm_device *dev, int pipe,
 					   uint32_t sprite_width,
 					   int pixel_size);
+extern void intel_update_linetime_watermarks(struct drm_device *dev, int pipe,
+			 struct drm_display_mode *mode);
 
 extern int intel_sprite_set_colorkey(struct drm_device *dev, void *data,
 				     struct drm_file *file_priv);

drivers/gpu/drm/i915/intel_pm.c

@@ -1883,6 +1883,33 @@ static void sandybridge_update_wm(struct drm_device *dev)
 		   cursor_wm);
 }
 
+static void
+haswell_update_linetime_wm(struct drm_device *dev, int pipe,
+				 struct drm_display_mode *mode)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	u32 temp;
+
+	temp = I915_READ(PIPE_WM_LINETIME(pipe));
+	temp &= ~PIPE_WM_LINETIME_MASK;
+
+	/* The WM are computed with base on how long it takes to fill a single
+	 * row at the given clock rate, multiplied by 8.
+	 * */
+	temp |= PIPE_WM_LINETIME_TIME(
+		((mode->crtc_hdisplay * 1000) / mode->clock) * 8);
+
+	/* IPS watermarks are only used by pipe A, and are ignored by
+	 * pipes B and C.  They are calculated similarly to the common
+	 * linetime values, except that we are using CD clock frequency
+	 * in MHz instead of pixel rate for the division.
+	 *
+	 * This is a placeholder for the IPS watermark calculation code.
+	 */
+
+	I915_WRITE(PIPE_WM_LINETIME(pipe), temp);
+}
+
 static bool
 sandybridge_compute_sprite_wm(struct drm_device *dev, int plane,
 			      uint32_t sprite_width, int pixel_size,
@@ -2078,6 +2105,15 @@ void intel_update_watermarks(struct drm_device *dev)
 		dev_priv->display.update_wm(dev);
 }
 
+void intel_update_linetime_watermarks(struct drm_device *dev,
+		int pipe, struct drm_display_mode *mode)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (dev_priv->display.update_linetime_wm)
+		dev_priv->display.update_linetime_wm(dev, pipe, mode);
+}
+
 void intel_update_sprite_watermarks(struct drm_device *dev, int pipe,
 				    uint32_t sprite_width, int pixel_size)
 {
@@ -3689,6 +3725,7 @@ void intel_init_pm(struct drm_device *dev)
 			if (SNB_READ_WM0_LATENCY()) {
 				dev_priv->display.update_wm = sandybridge_update_wm;
 				dev_priv->display.update_sprite_wm = sandybridge_update_sprite_wm;
+				dev_priv->display.update_linetime_wm = haswell_update_linetime_wm;
 			} else {
 				DRM_DEBUG_KMS("Failed to read display plane latency. "
 					      "Disable CxSR\n");