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>

1 files changed, 5 insertions, 9 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 087e76b9ee35..304f86a3162c 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/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,