[PATCH 2/2] drm/i915: Implement vblank synchronized MBUS join changes

Stanislav Lisovskiy stanislav.lisovskiy at intel.com
Wed Sep 20 12:22:08 UTC 2023


Currently we can't change MBUS join status without doing a modeset,
because we are lacking mechanism to synchronize those with vblank.
However then this means that we can't do a fastset, if there is a need
to change MBUS join state. Fix that by implementing such change.
We already call correspondent check and update at pre_plane dbuf update,
so the only thing left is to have a non-modeset version of that.
If active pipes stay the same then fastset is possible and only MBUS
join state/ddb allocation updates would be committed.

v2: Implement additional changes according to BSpec.
    Vblank wait is needed after MBus/Dbuf programming in case if
    no modeset is done and we are switching from single to multiple
    displays, i.e mbus join state switches from "joined" to  "non-joined"
    state. Otherwise vblank wait is not needed according to spec.

v3: Split mbus and dbox programming into to pre/post plane update parts,
    how it should be done according to BSpec.

v4: - Place "single display to multiple displays scenario" MBUS/DBOX programming
      after DDB reallocation, but before crtc enabling(that is where is has
      to be according to spec).
    - Check if crtc is still active, not only the old state.
    - Do a vblank wait if MBUX DBOX register was modified.
    - And of course do vblank wait only if crtc was active.
    - Do vblank wait only if we are not doing a modeset, if we are doing
      something before *commit_modeset_enables, because all crtcs might be
      disabled at this moment, so we will get WARN if try waiting for vblank
      then.
    - Still getting FIFO underrun so try waiting for vblank in pre_plane update
      as well.
    - Write also pipe that we need to sync with to MBUS_CTL register.

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c |  13 +-
 drivers/gpu/drm/i915/display/skl_watermark.c | 127 ++++++++++++++++---
 drivers/gpu/drm/i915/display/skl_watermark.h |   1 +
 3 files changed, 119 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 6bbc9069754c4..579988fb2bf5f 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -6769,6 +6769,17 @@ static void skl_commit_modeset_enables(struct intel_atomic_state *state)
 		}
 	}
 
+	/*
+	 * Some MBUS/DBuf update scenarios(mbus join disable) require that
+	 * changes are done _after_ DDB reallocation, but _before_ crtc enabling.
+	 * Typically we are disabling resources in post_plane/crtc_enable hooks,
+	 * however in that case BSpec explicitly states that this should be done
+	 * before we enable additional displays.
+	 * FIXME: Should we still call this also there(post_plane hook)
+	 * for extra-safety? If so, how to make sure, we don't call it twice?
+	 */
+	intel_dbuf_mbus_post_ddb_update(state);
+
 	update_pipes = modeset_pipes;
 
 	/*
@@ -7028,9 +7039,7 @@ static void intel_atomic_commit_tail(struct intel_atomic_state *state)
 	}
 
 	intel_encoders_update_prepare(state);
-
 	intel_dbuf_pre_plane_update(state);
-	intel_mbus_dbox_update(state);
 
 	for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i) {
 		if (new_crtc_state->do_async_flip)
diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
index af99f2abd8446..8cfc2279a1bdf 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.c
+++ b/drivers/gpu/drm/i915/display/skl_watermark.c
@@ -2614,13 +2614,6 @@ skl_compute_ddb(struct intel_atomic_state *state)
 		if (ret)
 			return ret;
 
-		if (old_dbuf_state->joined_mbus != new_dbuf_state->joined_mbus) {
-			/* TODO: Implement vblank synchronized MBUS joining changes */
-			ret = intel_modeset_all_pipes(state, "MBUS joining change");
-			if (ret)
-				return ret;
-		}
-
 		drm_dbg_kms(&i915->drm,
 			    "Enabled dbuf slices 0x%x -> 0x%x (total dbuf slices 0x%x), mbus joined? %s->%s\n",
 			    old_dbuf_state->enabled_slices,
@@ -3479,7 +3472,9 @@ static void intel_dbuf_mbus_update(struct intel_atomic_state *state)
 	struct drm_i915_private *i915 = to_i915(state->base.dev);
 	u32 mbus_ctl, dbuf_min_tracker_val;
 	enum dbuf_slice slice;
-	const struct intel_dbuf_state *dbuf_state =
+	const struct intel_dbuf_state *new_dbuf_state =
+		intel_atomic_get_new_dbuf_state(state);
+	const struct intel_dbuf_state *old_dbuf_state =
 		intel_atomic_get_new_dbuf_state(state);
 
 	if (!HAS_MBUS_JOINING(i915))
@@ -3489,13 +3484,33 @@ static void intel_dbuf_mbus_update(struct intel_atomic_state *state)
 	 * TODO: Implement vblank synchronized MBUS joining changes.
 	 * Must be properly coordinated with dbuf reprogramming.
 	 */
-	if (dbuf_state->joined_mbus) {
+	if (new_dbuf_state->joined_mbus) {
+		enum pipe pipe = ffs(new_dbuf_state->active_pipes) - 1;
+
 		mbus_ctl = MBUS_HASHING_MODE_1x4 | MBUS_JOIN |
-			MBUS_JOIN_PIPE_SELECT_NONE;
+			MBUS_JOIN_PIPE_SELECT(pipe);
 		dbuf_min_tracker_val = DBUF_MIN_TRACKER_STATE_SERVICE(3);
 	} else {
-		mbus_ctl = MBUS_HASHING_MODE_2x2 |
-			MBUS_JOIN_PIPE_SELECT_NONE;
+		/*
+		 * BSpec instructs us that even if we are swithing off.
+		 * mbus join, we should write previously single pipe here
+		 * However what if prev state didn't have mbus joined as well?
+		 * We have of course checks in pre/post_plane update, however
+		 * it can still be triggered, if something else besides mbus_join
+		 * got changed. So lets write *PIPE_SELECT_NONE by default to be
+		 * on safe side.
+		 */
+		if (old_dbuf_state->joined_mbus) {
+			enum pipe pipe;
+			pipe = ffs(old_dbuf_state->active_pipes) - 1;
+
+			mbus_ctl = MBUS_HASHING_MODE_2x2 |
+				MBUS_JOIN_PIPE_SELECT(pipe);
+		} else {
+			mbus_ctl = MBUS_HASHING_MODE_2x2 |
+				MBUS_JOIN_PIPE_SELECT_NONE;
+		}
+
 		dbuf_min_tracker_val = DBUF_MIN_TRACKER_STATE_SERVICE(1);
 	}
 
@@ -3524,8 +3539,33 @@ void intel_dbuf_pre_plane_update(struct intel_atomic_state *state)
 
 	WARN_ON(!new_dbuf_state->base.changed);
 
-	if (hweight8(new_dbuf_state->active_pipes) <= hweight8(old_dbuf_state->active_pipes))
+	/*
+	 * Switching from multiple to single display scenario(enable mbus join).
+	 * Also we put here "<=" instead of "<" for suboptimal cases, when
+	 * we switch from single => single display, enabling mbus join.
+	 */
+	if (hweight8(new_dbuf_state->active_pipes) <= hweight8(old_dbuf_state->active_pipes)) {
+		struct intel_crtc *crtc;
+		struct intel_crtc_state *old_crtc_state, *new_crtc_state;
+		int i;
+
 		intel_dbuf_mbus_update(state);
+		intel_mbus_dbox_update(state);
+
+		if (state->modeset)
+			return;
+
+		for_each_oldnew_intel_crtc_in_state(state, crtc, old_crtc_state,
+						    new_crtc_state, i) {
+			/*
+			 * According to BSpec we should wait vblank on previously single display
+			 */
+			if (!old_crtc_state->hw.active || !new_crtc_state->hw.active)
+				continue;
+
+			intel_crtc_wait_for_next_vblank(crtc);
+		}
+	}
 
 	gen9_dbuf_slices_update(i915,
 				old_dbuf_state->enabled_slices |
@@ -3547,13 +3587,50 @@ void intel_dbuf_post_plane_update(struct intel_atomic_state *state)
 
 	WARN_ON(!new_dbuf_state->base.changed);
 
-	if (hweight8(new_dbuf_state->active_pipes) > hweight8(old_dbuf_state->active_pipes))
-		intel_dbuf_mbus_update(state);
-
 	gen9_dbuf_slices_update(i915,
 				new_dbuf_state->enabled_slices);
 }
 
+void intel_dbuf_mbus_post_ddb_update(struct intel_atomic_state *state)
+{
+	const struct intel_dbuf_state *new_dbuf_state =
+		intel_atomic_get_new_dbuf_state(state);
+	const struct intel_dbuf_state *old_dbuf_state =
+		intel_atomic_get_old_dbuf_state(state);
+
+	if (!new_dbuf_state ||
+	    (new_dbuf_state->enabled_slices == old_dbuf_state->enabled_slices &&
+	     new_dbuf_state->joined_mbus == old_dbuf_state->joined_mbus))
+		return;
+
+	WARN_ON(!new_dbuf_state->base.changed);
+
+	/*
+	 * Switching from single to multiple display scenario
+	 */
+	if (hweight8(new_dbuf_state->active_pipes) > hweight8(old_dbuf_state->active_pipes)) {
+		struct intel_crtc *crtc;
+		struct intel_crtc_state *old_crtc_state, *new_crtc_state;
+		int i;
+		intel_dbuf_mbus_update(state);
+		intel_mbus_dbox_update(state);
+
+		if (state->modeset)
+			return;
+
+		for_each_oldnew_intel_crtc_in_state(state, crtc, old_crtc_state,
+						    new_crtc_state, i) {
+			/*
+			 * According to BSpec we should wait vblank on previously single display
+			 */
+			if (!old_crtc_state->hw.active || !new_crtc_state->hw.active)
+				continue;
+
+			intel_crtc_wait_for_next_vblank(crtc);
+		}
+	}
+}
+
 static bool xelpdp_is_only_pipe_per_dbuf_bank(enum pipe pipe, u8 active_pipes)
 {
 	switch (pipe) {
@@ -3577,8 +3654,8 @@ void intel_mbus_dbox_update(struct intel_atomic_state *state)
 {
 	struct drm_i915_private *i915 = to_i915(state->base.dev);
 	const struct intel_dbuf_state *new_dbuf_state, *old_dbuf_state;
-	const struct intel_crtc_state *new_crtc_state;
-	const struct intel_crtc *crtc;
+	const struct intel_crtc_state *new_crtc_state, *old_crtc_state;
+	struct intel_crtc *crtc;
 	u32 val = 0;
 	int i;
 
@@ -3624,12 +3701,14 @@ void intel_mbus_dbox_update(struct intel_atomic_state *state)
 		val |= MBUS_DBOX_B_CREDIT(8);
 	}
 
-	for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i) {
-		u32 pipe_val = val;
+	for_each_oldnew_intel_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
+		u32 pipe_val = val, old_pipe_val;
 
 		if (!new_crtc_state->hw.active)
 			continue;
 
+		old_pipe_val = intel_de_read(i915, PIPE_MBUS_DBOX_CTL(crtc->pipe));
+
 		if (DISPLAY_VER(i915) >= 14) {
 			if (xelpdp_is_only_pipe_per_dbuf_bank(crtc->pipe,
 							      new_dbuf_state->active_pipes))
@@ -3639,6 +3718,14 @@ void intel_mbus_dbox_update(struct intel_atomic_state *state)
 		}
 
 		intel_de_write(i915, PIPE_MBUS_DBOX_CTL(crtc->pipe), pipe_val);
+
+		/*
+		 * BSpec instructs us to wait for vblank, if credits were changed.
+		 * However we need to do that here only if crtc was active prior to change.
+		 */
+		if (old_pipe_val != pipe_val &&
+		    old_crtc_state->hw.active && !state->modeset)
+			intel_crtc_wait_for_next_vblank(crtc);
 	}
 }
 
diff --git a/drivers/gpu/drm/i915/display/skl_watermark.h b/drivers/gpu/drm/i915/display/skl_watermark.h
index f91a3d4ddc075..96a4eed1daceb 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.h
+++ b/drivers/gpu/drm/i915/display/skl_watermark.h
@@ -71,6 +71,7 @@ intel_atomic_get_dbuf_state(struct intel_atomic_state *state);
 int intel_dbuf_init(struct drm_i915_private *i915);
 void intel_dbuf_pre_plane_update(struct intel_atomic_state *state);
 void intel_dbuf_post_plane_update(struct intel_atomic_state *state);
+void intel_dbuf_mbus_post_ddb_update(struct intel_atomic_state *state);
 void intel_mbus_dbox_update(struct intel_atomic_state *state);
 
 #endif /* __SKL_WATERMARK_H__ */
-- 
2.37.3



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