drm/i915: Fix gen2 and hsw+ scanline counter

On gen2 the scanline counter behaves a bit differently from the
later generations. Instead of adding one to the raw scanline
counter value, we must subtract one.

On HSW/BDW the scanline counter requires a +2 adjustment on HDMI
outputs. DP outputs on the on the other require the typical +1
adjustment.

As the fixup we must apply to the hardware scanline counter
depends on several factors, compute the desired offset at modeset
time and tuck it away for when it's needed.

v2: Clarify HSW+ situation

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: "Akash Goel <akash.goels@gmail.com>"
Reviewed-by: "Sourab Gupta <sourabgupta@gmail.com>"
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78997
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -889,9 +889,9 @@ static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	const struct drm_display_mode *mode = &crtc->config.adjusted_mode;
 	enum pipe pipe = crtc->pipe;
-	int vtotal = mode->crtc_vtotal;
-	int position;
+	int position, vtotal;
 
+	vtotal = mode->crtc_vtotal;
 	if (mode->flags & DRM_MODE_FLAG_INTERLACE)
 		vtotal /= 2;
 
@@ -901,14 +901,10 @@ static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
 		position = __raw_i915_read32(dev_priv, PIPEDSL(pipe)) & DSL_LINEMASK_GEN3;
 
 	/*
-	 * Scanline counter increments at leading edge of hsync, and
-	 * it starts counting from vtotal-1 on the first active line.
-	 * That means the scanline counter value is always one less
-	 * than what we would expect. Ie. just after start of vblank,
-	 * which also occurs at start of hsync (on the last active line),
-	 * the scanline counter will read vblank_start-1.
+	 * See update_scanline_offset() for the details on the
+	 * scanline_offset adjustment.
 	 */
-	return (position + 1) % vtotal;
+	return (position + crtc->scanline_offset) % vtotal;
 }
 
 static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe,

drivers/gpu/drm/i915/intel_display.c

@@ -10231,6 +10231,44 @@ void ironlake_check_encoder_dotclock(const struct intel_crtc_config *pipe_config
 	     pipe_config->adjusted_mode.crtc_clock, dotclock);
 }
 
+static void update_scanline_offset(struct intel_crtc *crtc)
+{
+	struct drm_device *dev = crtc->base.dev;
+
+	/*
+	 * The scanline counter increments at the leading edge of hsync.
+	 *
+	 * On most platforms it starts counting from vtotal-1 on the
+	 * first active line. That means the scanline counter value is
+	 * always one less than what we would expect. Ie. just after
+	 * start of vblank, which also occurs at start of hsync (on the
+	 * last active line), the scanline counter will read vblank_start-1.
+	 *
+	 * On gen2 the scanline counter starts counting from 1 instead
+	 * of vtotal-1, so we have to subtract one (or rather add vtotal-1
+	 * to keep the value positive), instead of adding one.
+	 *
+	 * On HSW+ the behaviour of the scanline counter depends on the output
+	 * type. For DP ports it behaves like most other platforms, but on HDMI
+	 * there's an extra 1 line difference. So we need to add two instead of
+	 * one to the value.
+	 */
+	if (IS_GEN2(dev)) {
+		const struct drm_display_mode *mode = &crtc->config.adjusted_mode;
+		int vtotal;
+
+		vtotal = mode->crtc_vtotal;
+		if (mode->flags & DRM_MODE_FLAG_INTERLACE)
+			vtotal /= 2;
+
+		crtc->scanline_offset = vtotal - 1;
+	} else if (HAS_DDI(dev) &&
+		   intel_pipe_has_type(&crtc->base, INTEL_OUTPUT_HDMI)) {
+		crtc->scanline_offset = 2;
+	} else
+		crtc->scanline_offset = 1;
+}
+
 static int __intel_set_mode(struct drm_crtc *crtc,
 			    struct drm_display_mode *mode,
 			    int x, int y, struct drm_framebuffer *fb)
@@ -10349,8 +10387,11 @@ static int __intel_set_mode(struct drm_crtc *crtc,
 	}
 
 	/* Now enable the clocks, plane, pipe, and connectors that we set up. */
-	for_each_intel_crtc_masked(dev, prepare_pipes, intel_crtc)
+	for_each_intel_crtc_masked(dev, prepare_pipes, intel_crtc) {
+		update_scanline_offset(intel_crtc);
+
 		dev_priv->display.crtc_enable(&intel_crtc->base);
+	}
 
 	/* FIXME: add subpixel order */
 done:
@@ -11900,6 +11941,8 @@ static void intel_sanitize_crtc(struct intel_crtc *crtc)
 		 */
 		crtc->cpu_fifo_underrun_disabled = true;
 		crtc->pch_fifo_underrun_disabled = true;
+
+		update_scanline_offset(crtc);
 	}
 }
 

drivers/gpu/drm/i915/intel_drv.h

@@ -409,6 +409,8 @@ struct intel_crtc {
 	} wm;
 
 	wait_queue_head_t vbl_wait;
+
+	int scanline_offset;
 };
 
 struct intel_plane_wm_parameters {