drm/i915: Unconfuse pipe vs. crtc->index in i915_get_crtc_scanoutpos()

The "pipe" argument passed in by the vblank code is in fact the crtc
index. Don't assume that is the same as the pipe.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190821173033.24123-2-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/i915_irq.c

@@ -942,14 +942,14 @@ static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
 	return (position + crtc->scanline_offset) % vtotal;
 }
 
-bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int pipe,
+bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int index,
 			      bool in_vblank_irq, int *vpos, int *hpos,
 			      ktime_t *stime, ktime_t *etime,
 			      const struct drm_display_mode *mode)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
-	struct intel_crtc *intel_crtc = intel_get_crtc_for_pipe(dev_priv,
-								pipe);
+	struct intel_crtc *crtc = to_intel_crtc(drm_crtc_from_index(dev, index));
+	enum pipe pipe = crtc->pipe;
 	int position;
 	int vbl_start, vbl_end, hsync_start, htotal, vtotal;
 	unsigned long irqflags;
@@ -992,7 +992,7 @@ bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int pipe,
 		/* No obvious pixelcount register. Only query vertical
 		 * scanout position from Display scan line register.
 		 */
-		position = __intel_get_crtc_scanline(intel_crtc);
+		position = __intel_get_crtc_scanline(crtc);
 	} else {
 		/* Have access to pixelcount since start of frame.
 		 * We can split this into vertical and horizontal