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drm/vblank: do not halve the frame duration twice for interlaced modes #7542

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drm/vblank: do not halve the frame duration twice for interlaced modes #7542

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10 changes: 8 additions & 2 deletions drivers/gpu/drm/drm_vblank.c
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Original file line number Diff line number Diff line change
Expand Up @@ -649,9 +649,15 @@ void drm_calc_timestamping_constants(struct drm_crtc *crtc,
framedur_ns = div_u64((u64) frame_size * 1000000, dotclock);

/*
* Fields of interlaced scanout modes are only half a frame duration.
* Fields of interlaced scanout modes are only half a frame
* duration. Halving is only correct while the crtc timings
* still describe a whole frame: a driver that applied
* CRTC_INTERLACE_HALVE_V has already reduced crtc_vtotal to a
* single field, so frame_size above is a field already and
* halving it again reports half the real vblank interval.
*/
if (mode->flags & DRM_MODE_FLAG_INTERLACE)
if ((mode->flags & DRM_MODE_FLAG_INTERLACE) &&
mode->crtc_vtotal >= mode->vtotal)
framedur_ns /= 2;
} else {
drm_err(dev, "crtc %u: Can't calculate constants, dotclock = 0!\n",
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