drm/vblank: Allow dynamic per-crtc max_vblank_count

On i965gm we need to adjust max_vblank_count dynamically
depending on whether the TV encoder is used or not. To
that end add a per-crtc max_vblank_count that takes
precedence over its device wide counterpart. The driver
can now call drm_crtc_set_max_vblank_count() to configure
the per-crtc value before calling drm_vblank_on().

Also looks like there was some discussion about exynos needing
similar treatment.

v2: Drop the extra max_vblank_count!=0 check for the
    WARN(last!=current), will take care of it in i915 code (Daniel)
    WARN_ON(!inmodeset) (Daniel)
    WARN_ON(dev->max_vblank_count)
    Pimp up the docs (Daniel)

Cc: stable@vger.kernel.org
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181127182004.28885-1-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 22 insertions, 0 deletions

diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index 6ad9630d4f48..e528bb2f659d 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -129,6 +129,26 @@ struct drm_vblank_crtc {
 	 */
 	u32 last;
 	/**
+	 * @max_vblank_count:
+	 *
+	 * Maximum value of the vblank registers for this crtc. This value +1
+	 * will result in a wrap-around of the vblank register. It is used
+	 * by the vblank core to handle wrap-arounds.
+	 *
+	 * If set to zero the vblank core will try to guess the elapsed vblanks
+	 * between times when the vblank interrupt is disabled through
+	 * high-precision timestamps. That approach is suffering from small
+	 * races and imprecision over longer time periods, hence exposing a
+	 * hardware vblank counter is always recommended.
+	 *
+	 * This is the runtime configurable per-crtc maximum set through
+	 * drm_crtc_set_max_vblank_count(). If this is used the driver
+	 * must leave the device wide &drm_device.max_vblank_count at zero.
+	 *
+	 * If non-zero, &drm_crtc_funcs.get_vblank_counter must be set.
+	 */
+	u32 max_vblank_count;
+	/**
 	 * @inmodeset: Tracks whether the vblank is disabled due to a modeset.
 	 * For legacy driver bit 2 additionally tracks whether an additional
 	 * temporary vblank reference has been acquired to paper over the
@@ -206,4 +226,6 @@ bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
 void drm_calc_timestamping_constants(struct drm_crtc *crtc,
 				     const struct drm_display_mode *mode);
 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);
 #endif