drm: Stop using linedur_ns and pixeldur_ns for vblank timestamps

linedur_ns, and especially pixeldur_ns are becoming rather inaccurate
to be used for the vblank timestamp correction. With 4k@60 the pixel
duration is already below 2ns, so the amount of error due to the
truncation to nanoseconds is introducing quite a bit of error.

We can avoid such problems if we instead calculate the timestamp
delta_ns directly from the dislay timings, avoiding the use of
these intermediate truncated values.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
[danvet: Squash in fixup from Thierry Reding for amdgpu.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/amd/amdgpu/amdgpu_display.c

@@ -745,7 +745,8 @@ bool amdgpu_crtc_scaling_mode_fixup(struct drm_crtc *crtc,
  *
  */
 int amdgpu_get_crtc_scanoutpos(struct drm_device *dev, int crtc, unsigned int flags,
-			       int *vpos, int *hpos, ktime_t *stime, ktime_t *etime)
+			       int *vpos, int *hpos, ktime_t *stime, ktime_t *etime,
+			       const struct drm_display_mode *mode)
 {
 	u32 vbl = 0, position = 0;
 	int vbl_start, vbl_end, vtotal, ret = 0;
@@ -781,7 +782,7 @@ int amdgpu_get_crtc_scanoutpos(struct drm_device *dev, int crtc, unsigned int fl
 	}
 	else {
 		/* No: Fake something reasonable which gives at least ok results. */
-		vbl_start = adev->mode_info.crtcs[crtc]->base.hwmode.crtc_vdisplay;
+		vbl_start = mode->crtc_vdisplay;
 		vbl_end = 0;
 	}
 
@@ -797,7 +798,7 @@ int amdgpu_get_crtc_scanoutpos(struct drm_device *dev, int crtc, unsigned int fl
 
 	/* Inside "upper part" of vblank area? Apply corrective offset if so: */
 	if (in_vbl && (*vpos >= vbl_start)) {
-		vtotal = adev->mode_info.crtcs[crtc]->base.hwmode.crtc_vtotal;
+		vtotal = mode->crtc_vtotal;
 		*vpos = *vpos - vtotal;
 	}
 
@@ -819,8 +820,8 @@ int amdgpu_get_crtc_scanoutpos(struct drm_device *dev, int crtc, unsigned int fl
 	 * We only do this if DRM_CALLED_FROM_VBLIRQ.
 	 */
 	if ((flags & DRM_CALLED_FROM_VBLIRQ) && !in_vbl) {
-		vbl_start = adev->mode_info.crtcs[crtc]->base.hwmode.crtc_vdisplay;
-		vtotal = adev->mode_info.crtcs[crtc]->base.hwmode.crtc_vtotal;
+		vbl_start = mode->crtc_vdisplay;
+		vtotal = mode->crtc_vtotal;
 
 		if (vbl_start - *vpos < vtotal / 100) {
 			*vpos -= vtotal;

drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h

@@ -543,7 +543,8 @@ void amdgpu_encoder_set_active_device(struct drm_encoder *encoder);
 int amdgpu_get_crtc_scanoutpos(struct drm_device *dev, int crtc,
 				      unsigned int flags,
 				      int *vpos, int *hpos, ktime_t *stime,
-				      ktime_t *etime);
+				      ktime_t *etime,
+				      const struct drm_display_mode *mode);
 
 int amdgpu_framebuffer_init(struct drm_device *dev,
 			     struct amdgpu_framebuffer *rfb,

drivers/gpu/drm/drm_irq.c

@@ -694,12 +694,11 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
 					  unsigned flags,
 					  const struct drm_display_mode *mode)
 {
-	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
 	struct timeval tv_etime;
 	ktime_t stime, etime;
 	int vbl_status;
 	int vpos, hpos, i;
-	int framedur_ns, linedur_ns, pixeldur_ns, delta_ns, duration_ns;
+	int delta_ns, duration_ns;
 	bool invbl;
 
 	if (pipe >= dev->num_crtcs) {
@@ -713,15 +712,10 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
 		return -EIO;
 	}
 
-	/* Durations of frames, lines, pixels in nanoseconds. */
-	framedur_ns = vblank->framedur_ns;
-	linedur_ns  = vblank->linedur_ns;
-	pixeldur_ns = vblank->pixeldur_ns;
-
 	/* If mode timing undefined, just return as no-op:
 	 * Happens during initial modesetting of a crtc.
 	 */
-	if (framedur_ns == 0) {
+	if (mode->crtc_clock == 0) {
 		DRM_DEBUG("crtc %u: Noop due to uninitialized mode.\n", pipe);
 		return -EAGAIN;
 	}
@@ -738,8 +732,10 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
 		 * Get vertical and horizontal scanout position vpos, hpos,
 		 * and bounding timestamps stime, etime, pre/post query.
 		 */
-		vbl_status = dev->driver->get_scanout_position(dev, pipe, flags, &vpos,
-							       &hpos, &stime, &etime);
+		vbl_status = dev->driver->get_scanout_position(dev, pipe, flags,
+							       &vpos, &hpos,
+							       &stime, &etime,
+							       mode);
 
 		/* Return as no-op if scanout query unsupported or failed. */
 		if (!(vbl_status & DRM_SCANOUTPOS_VALID)) {
@@ -776,7 +772,8 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
 	 * since start of scanout at first display scanline. delta_ns
 	 * can be negative if start of scanout hasn't happened yet.
 	 */
-	delta_ns = vpos * linedur_ns + hpos * pixeldur_ns;
+	delta_ns = div_s64(1000000LL * (vpos * mode->crtc_htotal + hpos),
+			   mode->crtc_clock);
 
 	if (!drm_timestamp_monotonic)
 		etime = ktime_mono_to_real(etime);

drivers/gpu/drm/i915/i915_irq.c

@@ -648,12 +648,12 @@ static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
 
 static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe,
 				    unsigned int flags, int *vpos, int *hpos,
-				    ktime_t *stime, ktime_t *etime)
+				    ktime_t *stime, ktime_t *etime,
+				    const struct drm_display_mode *mode)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
-	const struct drm_display_mode *mode = &intel_crtc->base.hwmode;
 	int position;
 	int vbl_start, vbl_end, hsync_start, htotal, vtotal;
 	bool in_vbl = true;

drivers/gpu/drm/nouveau/nouveau_display.c

@@ -133,7 +133,8 @@ nouveau_display_scanoutpos_head(struct drm_crtc *crtc, int *vpos, int *hpos,
 
 int
 nouveau_display_scanoutpos(struct drm_device *dev, int head, unsigned int flags,
-			   int *vpos, int *hpos, ktime_t *stime, ktime_t *etime)
+			   int *vpos, int *hpos, ktime_t *stime, ktime_t *etime,
+			   const struct drm_display_mode *mode)
 {
 	struct drm_crtc *crtc;
 

drivers/gpu/drm/nouveau/nouveau_display.h

@@ -68,7 +68,8 @@ void nouveau_display_resume(struct drm_device *dev, bool runtime);
 int  nouveau_display_vblank_enable(struct drm_device *, int);
 void nouveau_display_vblank_disable(struct drm_device *, int);
 int  nouveau_display_scanoutpos(struct drm_device *, int, unsigned int,
-				int *, int *, ktime_t *, ktime_t *);
+				int *, int *, ktime_t *, ktime_t *,
+				const struct drm_display_mode *);
 int  nouveau_display_vblstamp(struct drm_device *, int, int *,
 			      struct timeval *, unsigned);
 

drivers/gpu/drm/radeon/radeon_display.c

@@ -323,7 +323,8 @@ void radeon_crtc_handle_vblank(struct radeon_device *rdev, int crtc_id)
 	 */
 	if (update_pending &&
 	    (DRM_SCANOUTPOS_VALID & radeon_get_crtc_scanoutpos(rdev->ddev, crtc_id, 0,
-							       &vpos, &hpos, NULL, NULL)) &&
+							       &vpos, &hpos, NULL, NULL,
+							       &rdev->mode_info.crtcs[crtc_id]->base.hwmode)) &&
 	    ((vpos >= (99 * rdev->mode_info.crtcs[crtc_id]->base.hwmode.crtc_vdisplay)/100) ||
 	     (vpos < 0 && !ASIC_IS_AVIVO(rdev)))) {
 		/* crtc didn't flip in this target vblank interval,
@@ -1799,7 +1800,8 @@ bool radeon_crtc_scaling_mode_fixup(struct drm_crtc *crtc,
  *
  */
 int radeon_get_crtc_scanoutpos(struct drm_device *dev, int crtc, unsigned int flags,
-			       int *vpos, int *hpos, ktime_t *stime, ktime_t *etime)
+			       int *vpos, int *hpos, ktime_t *stime, ktime_t *etime,
+			       const struct drm_display_mode *mode)
 {
 	u32 stat_crtc = 0, vbl = 0, position = 0;
 	int vbl_start, vbl_end, vtotal, ret = 0;
@@ -1914,7 +1916,7 @@ int radeon_get_crtc_scanoutpos(struct drm_device *dev, int crtc, unsigned int fl
 	}
 	else {
 		/* No: Fake something reasonable which gives at least ok results. */
-		vbl_start = rdev->mode_info.crtcs[crtc]->base.hwmode.crtc_vdisplay;
+		vbl_start = mode->crtc_vdisplay;
 		vbl_end = 0;
 	}
 
@@ -1930,7 +1932,7 @@ int radeon_get_crtc_scanoutpos(struct drm_device *dev, int crtc, unsigned int fl
 
 	/* Inside "upper part" of vblank area? Apply corrective offset if so: */
 	if (in_vbl && (*vpos >= vbl_start)) {
-		vtotal = rdev->mode_info.crtcs[crtc]->base.hwmode.crtc_vtotal;
+		vtotal = mode->crtc_vtotal;
 		*vpos = *vpos - vtotal;
 	}
 
@@ -1952,8 +1954,8 @@ int radeon_get_crtc_scanoutpos(struct drm_device *dev, int crtc, unsigned int fl
 	 * We only do this if DRM_CALLED_FROM_VBLIRQ.
 	 */
 	if ((flags & DRM_CALLED_FROM_VBLIRQ) && !in_vbl) {
-		vbl_start = rdev->mode_info.crtcs[crtc]->base.hwmode.crtc_vdisplay;
-		vtotal = rdev->mode_info.crtcs[crtc]->base.hwmode.crtc_vtotal;
+		vbl_start = mode->crtc_vdisplay;
+		vtotal = mode->crtc_vtotal;
 
 		if (vbl_start - *vpos < vtotal / 100) {
 			*vpos -= vtotal;

drivers/gpu/drm/radeon/radeon_drv.c

@@ -126,8 +126,9 @@ struct dma_buf *radeon_gem_prime_export(struct drm_device *dev,
 					int flags);
 extern int radeon_get_crtc_scanoutpos(struct drm_device *dev, int crtc,
 				      unsigned int flags,
-				      int *vpos, int *hpos, ktime_t *stime,
-				      ktime_t *etime);
+				      int *vpos, int *hpos,
+				      ktime_t *stime, ktime_t *etime,
+				      const struct drm_display_mode *mode);
 extern bool radeon_is_px(struct drm_device *dev);
 extern const struct drm_ioctl_desc radeon_ioctls_kms[];
 extern int radeon_max_kms_ioctl;

drivers/gpu/drm/radeon/radeon_mode.h

@@ -876,8 +876,9 @@ extern void radeon_cursor_reset(struct drm_crtc *crtc);
 
 extern int radeon_get_crtc_scanoutpos(struct drm_device *dev, int crtc,
 				      unsigned int flags,
-				      int *vpos, int *hpos, ktime_t *stime,
-				      ktime_t *etime);
+				      int *vpos, int *hpos,
+				      ktime_t *stime, ktime_t *etime,
+				      const struct drm_display_mode *mode);
 
 extern bool radeon_combios_check_hardcoded_edid(struct radeon_device *rdev);
 extern struct edid *

drivers/gpu/drm/radeon/radeon_pm.c

@@ -1733,7 +1733,9 @@ static bool radeon_pm_in_vbl(struct radeon_device *rdev)
 	 */
 	for (crtc = 0; (crtc < rdev->num_crtc) && in_vbl; crtc++) {
 		if (rdev->pm.active_crtcs & (1 << crtc)) {
-			vbl_status = radeon_get_crtc_scanoutpos(rdev->ddev, crtc, 0, &vpos, &hpos, NULL, NULL);
+			vbl_status = radeon_get_crtc_scanoutpos(rdev->ddev, crtc, 0,
+								&vpos, &hpos, NULL, NULL,
+								&rdev->mode_info.crtcs[crtc]->base.hwmode);
 			if ((vbl_status & DRM_SCANOUTPOS_VALID) &&
 			    !(vbl_status & DRM_SCANOUTPOS_IN_VBLANK))
 				in_vbl = false;

include/drm/drmP.h

@@ -482,6 +482,7 @@ struct drm_driver {
 	 *               scanout position query. Can be NULL to skip timestamp.
 	 * \param *etime Target location for timestamp taken immediately after
 	 *               scanout position query. Can be NULL to skip timestamp.
+	 * \param mode Current display timings.
 	 *
 	 * Returns vpos as a positive number while in active scanout area.
 	 * Returns vpos as a negative number inside vblank, counting the number
@@ -499,8 +500,9 @@ struct drm_driver {
 	 */
 	int (*get_scanout_position) (struct drm_device *dev, int crtc,
 				     unsigned int flags,
-				     int *vpos, int *hpos, ktime_t *stime,
-				     ktime_t *etime);
+				     int *vpos, int *hpos,
+				     ktime_t *stime, ktime_t *etime,
+				     const struct drm_display_mode *mode);
 
 	/**
 	 * Called by \c drm_get_last_vbltimestamp. Should return a precise