On top of the interlaced video mode fix and with some additional
adjustments, this now works well. It has almost the same accuracy
as on regular progressive scan modes.

Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
Cc: Eric Anholt <eric at anholt.net>
---
 drivers/gpu/drm/vc4/vc4_crtc.c | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
index 2bfa247..7ffdad5 100644
--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -163,14 +163,6 @@ int vc4_crtc_get_scanoutpos(struct drm_device *dev, 
unsigned int crtc_id,
        int vblank_lines;
        int ret = 0;

-       /*
-        * XXX Doesn't work well in interlaced mode yet, partially due
-        * to problems in vc4 kms or drm core interlaced mode handling,
-        * so disable for now in interlaced mode.
-        */
-       if (mode->flags & DRM_MODE_FLAG_INTERLACE)
-               return ret;
-
        /* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */

        /* Get optional system timestamp before query. */
@@ -191,10 +183,15 @@ int vc4_crtc_get_scanoutpos(struct drm_device *dev, 
unsigned int crtc_id,

        /* Vertical position of hvs composed scanline. */
        *vpos = VC4_GET_FIELD(val, SCALER_DISPSTATX_LINE);
+       *hpos = 0;
+
+       if (mode->flags & DRM_MODE_FLAG_INTERLACE) {
+               *vpos /= 2;

-       /* No hpos info available. */
-       if (hpos)
-               *hpos = 0;
+               /* Use hpos to correct for field offset in interlaced mode. */
+               if (VC4_GET_FIELD(val, SCALER_DISPSTATX_FRAME_COUNT) % 2)
+                       *hpos += mode->crtc_htotal / 2;
+       }

        /* This is the offset we need for translating hvs -> pv scanout pos. */
        fifo_lines = vc4_crtc->cob_size / mode->crtc_hdisplay;
@@ -217,8 +214,6 @@ int vc4_crtc_get_scanoutpos(struct drm_device *dev, 
unsigned int crtc_id,
                 * position of the PV.
                 */
                *vpos -= fifo_lines + 1;
-               if (mode->flags & DRM_MODE_FLAG_INTERLACE)
-                       *vpos /= 2;

                ret |= DRM_SCANOUTPOS_ACCURATE;
                return ret;
-- 
2.7.0

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