drm: Add get_scanout_position() to struct drm_crtc_helper_funcs

The new callback get_scanout_position() reads the current location
of the scanout process. The operation is currently located in struct
drm_driver, but really belongs to the CRTC. Drivers will be converted
in separate patches.

To help with the conversion, the timestamp calculation has been
moved from drm_calc_vbltimestamp_from_scanoutpos() to
drm_crtc_vblank_helper_get_vblank_timestamp_internal(). The helper
function supports the new and old interface of get_scanout_position().
drm_calc_vbltimestamp_from_scanoutpos() remains as a wrapper around
the new function.

Callback functions return the scanout position from the CRTC. The
legacy version of the interface receives the device and pipe index,
the modern version receives a pointer to the CRTC. We keep the
legacy version until all drivers have been converted.

v4:
* 80-character line fixes
v3:
* refactor drm_calc_vbltimestamp_from_scanoutpos() to minimize
code duplication
* define types for get_scanout_position() callbacks
v2:
* fix logical op in drm_calc_vbltimestamp_from_scanoutpos()

Signed-off-by: Thomas Zimmermann <[e-mail]>
Tested-by: Yannick Fertré <[e-mail]>
Reviewed-by: Ville Syrjälä <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_vblank.c

···
 #include <drm/drm_crtc.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_framebuffer.h>
+#include <drm/drm_modeset_helper_vtables.h>
 #include <drm/drm_print.h>
 #include <drm/drm_vblank.h>
 
···
  * Implements calculation of exact vblank timestamps from given drm_display_mode
  * timings and current video scanout position of a CRTC. This can be directly
  * used as the &drm_driver.get_vblank_timestamp implementation of a kms driver
- * if &drm_driver.get_scanout_position is implemented.
+ * if &drm_crtc_helper_funcs.get_scanout_position is implemented.
  *
  * The current implementation only handles standard video modes. For double scan
  * and interlaced modes the driver is supposed to adjust the hardware mode
···
 					   ktime_t *vblank_time,
 					   bool in_vblank_irq)
 {
-	struct timespec64 ts_etime, ts_vblank_time;
-	ktime_t stime, etime;
-	bool vbl_status;
 	struct drm_crtc *crtc;
-	const struct drm_display_mode *mode;
-	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
-	int vpos, hpos, i;
-	int delta_ns, duration_ns;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return false;
 
 	crtc = drm_crtc_from_index(dev, pipe);
+	if (!crtc)
+		return false;
 
-	if (pipe >= dev->num_crtcs || !crtc) {
+	return drm_crtc_vblank_helper_get_vblank_timestamp_internal(crtc,
+								    max_error,
+								    vblank_time,
+								    in_vblank_irq,
+								    crtc->helper_private->get_scanout_position,
+								    dev->driver->get_scanout_position);
+}
+EXPORT_SYMBOL(drm_calc_vbltimestamp_from_scanoutpos);
+
+/**
+ * drm_crtc_vblank_helper_get_vblank_timestamp_internal - precise vblank
+ *                                                        timestamp helper
+ * @dev: DRM device
+ * @pipe: index of CRTC whose vblank timestamp to retrieve
+ * @max_error: Desired maximum allowable error in timestamps (nanosecs)
+ *             On return contains true maximum error of timestamp
+ * @vblank_time: Pointer to time which should receive the timestamp
+ * @in_vblank_irq:
+ *     True when called from drm_crtc_handle_vblank().  Some drivers
+ *     need to apply some workarounds for gpu-specific vblank irq quirks
+ *     if flag is set.
+ * @get_scanout_position:
+ *     Callback function to retrieve the scanout position. See
+ *     @struct drm_crtc_helper_funcs.get_scanout_position.
+ * @get_scanout_position_legacy:
+ *     Callback function to retrieve the scanout position. See
+ *     @struct drm_driver.get_scanout_position.
+ *
+ * Implements calculation of exact vblank timestamps from given drm_display_mode
+ * timings and current video scanout position of a CRTC.
+ *
+ * The current implementation only handles standard video modes. For double scan
+ * and interlaced modes the driver is supposed to adjust the hardware mode
+ * (taken from &drm_crtc_state.adjusted mode for atomic modeset drivers) to
+ * match the scanout position reported.
+ *
+ * Note that atomic drivers must call drm_calc_timestamping_constants() before
+ * enabling a CRTC. The atomic helpers already take care of that in
+ * drm_atomic_helper_update_legacy_modeset_state().
+ *
+ * Returns:
+ *
+ * Returns true on success, and false on failure, i.e. when no accurate
+ * timestamp could be acquired.
+ */
+bool
+drm_crtc_vblank_helper_get_vblank_timestamp_internal(
+	struct drm_crtc *crtc, int *max_error, ktime_t *vblank_time,
+	bool in_vblank_irq,
+	drm_vblank_get_scanout_position_func get_scanout_position,
+	drm_vblank_get_scanout_position_legacy_func get_scanout_position_legacy)
+{
+	struct drm_device *dev = crtc->dev;
+	unsigned int pipe = crtc->index;
+	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+	struct timespec64 ts_etime, ts_vblank_time;
+	ktime_t stime, etime;
+	bool vbl_status;
+	const struct drm_display_mode *mode;
+	int vpos, hpos, i;
+	int delta_ns, duration_ns;
+
+	if (pipe >= dev->num_crtcs) {
 		DRM_ERROR("Invalid crtc %u\n", pipe);
 		return false;
 	}
 
 	/* Scanout position query not supported? Should not happen. */
-	if (!dev->driver->get_scanout_position) {
-		DRM_ERROR("Called from driver w/o get_scanout_position()!?\n");
+	if (!get_scanout_position && !get_scanout_position_legacy) {
+		DRM_ERROR("Called from CRTC w/o get_scanout_position()!?\n");
 		return false;
 	}
 
···
 	if (mode->crtc_clock == 0) {
 		DRM_DEBUG("crtc %u: Noop due to uninitialized mode.\n", pipe);
 		WARN_ON_ONCE(drm_drv_uses_atomic_modeset(dev));
-
 		return false;
 	}
 
···
 		 * 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,
-							       in_vblank_irq,
-							       &vpos, &hpos,
-							       &stime, &etime,
-							       mode);
+		if (get_scanout_position) {
+			vbl_status = get_scanout_position(crtc,
+							  in_vblank_irq,
+							  &vpos, &hpos,
+							  &stime, &etime,
+							  mode);
+		} else {
+			vbl_status = get_scanout_position_legacy(dev, pipe,
+								 in_vblank_irq,
+								 &vpos, &hpos,
+								 &stime, &etime,
+								 mode);
+		}
 
 		/* Return as no-op if scanout query unsupported or failed. */
 		if (!vbl_status) {
···
 
 	return true;
 }
-EXPORT_SYMBOL(drm_calc_vbltimestamp_from_scanoutpos);
+EXPORT_SYMBOL(drm_crtc_vblank_helper_get_vblank_timestamp_internal);
 
 /**
  * drm_get_last_vbltimestamp - retrieve raw timestamp for the most recent

include/drm/drm_drv.h

···
 	 * True on success, false if a reliable scanout position counter could
 	 * not be read out.
 	 *
-	 * FIXME:
-	 *
-	 * Since this is a helper to implement @get_vblank_timestamp, we should
-	 * move it to &struct drm_crtc_helper_funcs, like all the other
-	 * helper-internal hooks.
+	 * This is deprecated and should not be used by new drivers.
+	 * Use &drm_crtc_helper_funcs.get_scanout_position instead.
 	 */
 	bool (*get_scanout_position) (struct drm_device *dev, unsigned int pipe,
 				      bool in_vblank_irq, int *vpos, int *hpos,

include/drm/drm_modeset_helper_vtables.h

···
 	 */
 	void (*atomic_disable)(struct drm_crtc *crtc,
 			       struct drm_crtc_state *old_crtc_state);
+
+	/**
+	 * @get_scanout_position:
+	 *
+	 * Called by vblank timestamping code.
+	 *
+	 * Returns the current display scanout position from a CRTC and an
+	 * optional accurate ktime_get() timestamp of when the position was
+	 * measured. Note that this is a helper callback which is only used
+	 * if a driver uses drm_calc_vbltimestamp_from_scanoutpos() for the
+	 * @drm_driver.get_vblank_timestamp callback.
+	 *
+	 * Parameters:
+	 *
+	 * crtc:
+	 *     The CRTC.
+	 * in_vblank_irq:
+	 *     True when called from drm_crtc_handle_vblank(). Some drivers
+	 *     need to apply some workarounds for gpu-specific vblank irq
+	 *     quirks if the flag is set.
+	 * vpos:
+	 *     Target location for current vertical scanout position.
+	 * hpos:
+	 *     Target location for current horizontal scanout position.
+	 * stime:
+	 *     Target location for timestamp taken immediately before
+	 *     scanout position query. Can be NULL to skip timestamp.
+	 * etime:
+	 *     Target location for timestamp taken immediately after
+	 *     scanout position query. Can be NULL to skip timestamp.
+	 * 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
+	 * of scanlines to go until end of vblank, e.g., -1 means "one scanline
+	 * until start of active scanout / end of vblank."
+	 *
+	 * Returns:
+	 *
+	 * True on success, false if a reliable scanout position counter could
+	 * not be read out.
+	 */
+	bool (*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);
 };
 
 /**

include/drm/drm_vblank.h

···
 wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc);
 void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
 				   u32 max_vblank_count);
+
+typedef bool (*drm_vblank_get_scanout_position_func)(struct drm_crtc *crtc,
+						     bool in_vblank_irq,
+						     int *vpos, int *hpos,
+						     ktime_t *stime,
+						     ktime_t *etime,
+						     const struct drm_display_mode *mode);
+
+typedef bool (*drm_vblank_get_scanout_position_legacy_func)(struct drm_device *dev,
+							    unsigned int pipe,
+							    bool in_vblank_irq,
+							    int *vpos,
+							    int *hpos,
+							    ktime_t *stime,
+							    ktime_t *etime,
+							    const struct drm_display_mode *mode);
+
+bool
+drm_crtc_vblank_helper_get_vblank_timestamp_internal(struct drm_crtc *crtc,
+						     int *max_error,
+						     ktime_t *vblank_time,
+						     bool in_vblank_irq,
+						     drm_vblank_get_scanout_position_func get_scanout_position,
+						     drm_vblank_get_scanout_position_legacy_func get_scanout_position_legacy);
+
 #endif