[PATCH 2/2] drm/vc4: crtc: Keep the previously assigned HVS FIFO

[Maxime Ripard]

The HVS FIFOs are currently assigned each time we have an atomic_check
for all the enabled CRTCs.

However, if we are running multiple outputs in parallel and we happen to
disable the first (by index) CRTC, we end up changing the assigned FIFO
of the second CRTC without disabling and reenabling the pixelvalve which
ends up in a stall and eventually a VBLANK timeout.

In order to fix this, we can create a special value for our assigned
channel to mark it as disabled, and if our CRTC already had an assigned
channel in its previous state, we keep on using it.

Fixes: 87ebcd42fb7b ("drm/vc4: crtc: Assign output to channel automatically")
Signed-off-by: Maxime Ripard <maxime at cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_crtc.c | 13 ++++++++++---
 drivers/gpu/drm/vc4/vc4_drv.h  |  1 +
 drivers/gpu/drm/vc4/vc4_kms.c  | 21 +++++++++++++++------
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
index a393f93390a2..be754120faa8 100644
--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -852,11 +852,18 @@ void vc4_crtc_destroy_state(struct drm_crtc *crtc,
 
 void vc4_crtc_reset(struct drm_crtc *crtc)
 {
+	struct vc4_crtc_state *vc4_crtc_state;
+
 	if (crtc->state)
 		vc4_crtc_destroy_state(crtc, crtc->state);
-	crtc->state = kzalloc(sizeof(struct vc4_crtc_state), GFP_KERNEL);
-	if (crtc->state)
-		__drm_atomic_helper_crtc_reset(crtc, crtc->state);
+
+	vc4_crtc_state = kzalloc(sizeof(*vc4_crtc_state), GFP_KERNEL);
+	if (!vc4_crtc_state)
+		return;
+
+	vc4_crtc_state->assigned_channel = VC4_HVS_CHANNEL_DISABLED;
+	crtc->state = &vc4_crtc_state->base;
+	__drm_atomic_helper_crtc_reset(crtc, crtc->state);
 }
 
 static const struct drm_crtc_funcs vc4_crtc_funcs = {
diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
index 8c8d96b6289f..2b13f2126f13 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.h
+++ b/drivers/gpu/drm/vc4/vc4_drv.h
@@ -531,6 +531,7 @@ struct vc4_crtc_state {
 		unsigned int bottom;
 	} margins;
 };
+#define VC4_HVS_CHANNEL_DISABLED ((unsigned int) -1)
 
 static inline struct vc4_crtc_state *
 to_vc4_crtc_state(struct drm_crtc_state *crtc_state)
diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index 01fa60844695..f452dad50c22 100644
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -616,7 +616,7 @@ static int
 vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 {
 	unsigned long unassigned_channels = GENMASK(NUM_CHANNELS - 1, 0);
-	struct drm_crtc_state *crtc_state;
+	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
 	struct drm_crtc *crtc;
 	int i, ret;
 
@@ -629,6 +629,7 @@ vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 	 * modified.
 	 */
 	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
+		struct drm_crtc_state *crtc_state;
 		if (!crtc->state->enable)
 			continue;
 
@@ -637,15 +638,23 @@ vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 			return PTR_ERR(crtc_state);
 	}
 
-	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
-		struct vc4_crtc_state *vc4_crtc_state =
-			to_vc4_crtc_state(crtc_state);
+	for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
+		struct vc4_crtc_state *new_vc4_crtc_state =
+			to_vc4_crtc_state(new_crtc_state);
 		struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
 		unsigned int matching_channels;
 
-		if (!crtc_state->enable)
+		if (old_crtc_state->enable && !new_crtc_state->enable)
+			new_vc4_crtc_state->assigned_channel = VC4_HVS_CHANNEL_DISABLED;
+
+		if (!new_crtc_state->enable)
 			continue;
 
+		if (new_vc4_crtc_state->assigned_channel != VC4_HVS_CHANNEL_DISABLED) {
+			unassigned_channels &= ~BIT(new_vc4_crtc_state->assigned_channel);
+			continue;
+		}
+
 		/*
 		 * The problem we have to solve here is that we have
 		 * up to 7 encoders, connected to up to 6 CRTCs.
@@ -674,7 +683,7 @@ vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 		if (matching_channels) {
 			unsigned int channel = ffs(matching_channels) - 1;
 
-			vc4_crtc_state->assigned_channel = channel;
+			new_vc4_crtc_state->assigned_channel = channel;
 			unassigned_channels &= ~BIT(channel);
 		} else {
 			return -EINVAL;
-- 
2.26.2