openmptcprouter/root/target/linux/bcm27xx/patches-5.15/0614-drm-vc4-kms-Fix-previous-HVS-commit-wait.patch

From dd7d827b5466f4820a477484c25a28a309d43b20 Mon Sep 17 00:00:00 2001
From: Maxime Ripard <maxime@cerno.tech>
Date: Fri, 5 Nov 2021 10:51:25 +0100
Subject: [PATCH 614/634] drm/vc4: kms: Fix previous HVS commit wait

Our current code is supposed to serialise the commits by waiting for all
the drm_crtc_commits associated to the previous HVS state.

However, assuming we have two CRTCs running and being configured and we
configure each one alternatively, we end up in a situation where we're
not waiting at all.

Indeed, starting with a state (state 0) where both CRTCs are running,
and doing a commit (state 1) on the first CRTC (CRTC 0), we'll associate
its commit to its assigned FIFO in vc4_hvs_state.

If we get a new commit (state 2), this time affecting the second CRTC
(CRTC 1), the DRM core will allow both commits to execute in parallel
(assuming they don't have any share resources).

Our code in vc4_atomic_commit_tail is supposed to make sure we only get
one commit at a time and serialised by order of submission. It does so
by using for_each_old_crtc_in_state, making sure that the CRTC has a
FIFO assigned, is used, and has a commit pending. If it does, then we'll
wait for the commit before going forward.

During the transition from state 0 to state 1, as our old CRTC state we
get the CRTC 0 state 0, its commit, we wait for it, everything works fine.

During the transition from state 1 to state 2 though, the use of
for_each_old_crtc_in_state is wrong. Indeed, while the code assumes it's
returning the state of the CRTC in the old state (so CRTC 0 state 1), it
actually returns the old state of the CRTC affected by the current
commit, so CRTC 0 state 0 since it wasn't part of state 1.

Due to this, if we alternate between the configuration of CRTC 0 and
CRTC 1, we never actually wait for anything since we should be waiting
on the other every time, but it never is affected by the previous
commit.

Change the logic to, at every commit, look at every FIFO in the previous
HVS state, and if it's in use and has a commit associated to it, wait
for that commit.

Fixes: 9ec03d7f1ed3 ("drm/vc4: kms: Wait on previous FIFO users before a commit")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_kms.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index 2ac6c7c66fc2..2721a0f61dc0 100644
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -343,12 +343,12 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
 	struct drm_device *dev = state->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	struct vc4_hvs *hvs = vc4->hvs;
-	struct drm_crtc_state *old_crtc_state;
 	struct drm_crtc_state *new_crtc_state;
 	struct vc4_hvs_state *new_hvs_state;
 	struct drm_crtc *crtc;
 	struct vc4_hvs_state *old_hvs_state;
 	struct clk_request *core_req;
+	unsigned int channel;
 	int i;
 
 	old_hvs_state = vc4_hvs_get_old_global_state(state);
@@ -369,16 +369,10 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
 		vc4_hvs_mask_underrun(dev, vc4_crtc_state->assigned_channel);
 	}
 
-	for_each_old_crtc_in_state(state, crtc, old_crtc_state, i) {
-		struct vc4_crtc_state *vc4_crtc_state =
-			to_vc4_crtc_state(old_crtc_state);
+	for (channel = 0; channel < HVS_NUM_CHANNELS; channel++) {
 		struct drm_crtc_commit *commit;
-		unsigned int channel = vc4_crtc_state->assigned_channel;
 		int ret;
 
-		if (channel == VC4_HVS_CHANNEL_DISABLED)
-			continue;
-
 		if (!old_hvs_state->fifo_state[channel].in_use)
 			continue;
 
-- 
2.33.1