drm/mgag200: Implement struct drm_crtc_funcs.get_vblank_timestamp

Implement struct drm_crtc_funcs.get_vblank_timestamp with the DRM
helper drm_crtc_vblank_helper_get_vblank_timestamp() with its helper
get_scanout_position. Read the scanout position from the MGAREG_VCOUNT
register.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240718104551.575912-8-tzimmermann@suse.de

drivers/gpu/drm/mgag200/mgag200_drv.h

@@ -400,13 +400,18 @@ int mgag200_crtc_helper_atomic_check(struct drm_crtc *crtc, struct drm_atomic_st
 void mgag200_crtc_helper_atomic_flush(struct drm_crtc *crtc, struct drm_atomic_state *old_state);
 void mgag200_crtc_helper_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_state *old_state);
 void mgag200_crtc_helper_atomic_disable(struct drm_crtc *crtc, struct drm_atomic_state *old_state);
+bool mgag200_crtc_helper_get_scanout_position(struct drm_crtc *crtc, bool in_vblank_irq,
+					      int *vpos, int *hpos,
+					      ktime_t *stime, ktime_t *etime,
+					      const struct drm_display_mode *mode);
 
 #define MGAG200_CRTC_HELPER_FUNCS \
 	.mode_valid = mgag200_crtc_helper_mode_valid, \
 	.atomic_check = mgag200_crtc_helper_atomic_check, \
 	.atomic_flush = mgag200_crtc_helper_atomic_flush, \
 	.atomic_enable = mgag200_crtc_helper_atomic_enable, \
-	.atomic_disable = mgag200_crtc_helper_atomic_disable
+	.atomic_disable = mgag200_crtc_helper_atomic_disable, \
+	.get_scanout_position = mgag200_crtc_helper_get_scanout_position
 
 void mgag200_crtc_reset(struct drm_crtc *crtc);
 struct drm_crtc_state *mgag200_crtc_atomic_duplicate_state(struct drm_crtc *crtc);
@@ -422,7 +427,8 @@ void mgag200_crtc_disable_vblank(struct drm_crtc *crtc);
 	.atomic_duplicate_state = mgag200_crtc_atomic_duplicate_state, \
 	.atomic_destroy_state = mgag200_crtc_atomic_destroy_state, \
 	.enable_vblank = mgag200_crtc_enable_vblank, \
-	.disable_vblank = mgag200_crtc_disable_vblank
+	.disable_vblank = mgag200_crtc_disable_vblank, \
+	.get_vblank_timestamp = drm_crtc_vblank_helper_get_vblank_timestamp
 
 void mgag200_set_mode_regs(struct mga_device *mdev, const struct drm_display_mode *mode,
 			   bool set_vidrst);

drivers/gpu/drm/mgag200/mgag200_mode.c

@@ -714,6 +714,31 @@ void mgag200_crtc_helper_atomic_disable(struct drm_crtc *crtc, struct drm_atomic
 	mgag200_disable_display(mdev);
 }
 
+bool mgag200_crtc_helper_get_scanout_position(struct drm_crtc *crtc, bool in_vblank_irq,
+					      int *vpos, int *hpos,
+					      ktime_t *stime, ktime_t *etime,
+					      const struct drm_display_mode *mode)
+{
+	struct mga_device *mdev = to_mga_device(crtc->dev);
+	u32 vcount;
+
+	if (stime)
+		*stime = ktime_get();
+
+	if (vpos) {
+		vcount = RREG32(MGAREG_VCOUNT);
+		*vpos = vcount & GENMASK(11, 0);
+	}
+
+	if (hpos)
+		*hpos = mode->htotal >> 1; // near middle of scanline on average
+
+	if (etime)
+		*etime = ktime_get();
+
+	return true;
+}
+
 void mgag200_crtc_reset(struct drm_crtc *crtc)
 {
 	struct mgag200_crtc_state *mgag200_crtc_state;