linux-kernel - [PATCH] drm/vkms: modify sequence disable/plane/enable in commit

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Message-Id: <20200729152231.13249-1-realwakka@gmail.com>
Date:   Wed, 29 Jul 2020 15:22:31 +0000
From:   Sidong Yang <realwakka@...il.com>
To:     Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>
Cc:     Sidong Yang <realwakka@...il.com>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kernel-usp@...glegroups.com
Subject: [PATCH] drm/vkms: modify sequence disable/plane/enable in commit_tail

This patch modifies function call sequence in commit tail. This is for
the problem that raised when kms_cursor_crc test is tested repeatedly.
In second test, there is an bug that crtc commit doesn't start vblank events.
Because there is some error about vblank's refcount. in commit_flush() that
called from commit_plane, drm_vblank_get() is called and vblank is enabled
in normal case. But in second test, vblank isn't enable for vblank->refcount
is already increased in previous test. Increased refcount will be decreased
in drm_atomic_helper_commit_modeset_enables() after commit_plane.
Therefore, commit_plane should be called after commit_modeset_enable.

In this situation, there is a warning raised in get_vblank_timestamp().
hrtimer.node.expires and vblank->time are zero for no vblank events before.
This patch returns current time when vblank is not enabled.

Cc: Daniel Vetter <daniel@...ll.ch>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
Cc: Haneen Mohammed <hamohammed.sa@...il.com>

Signed-off-by: Sidong Yang <realwakka@...il.com>
---
 drivers/gpu/drm/vkms/vkms_crtc.c | 5 +++++
 drivers/gpu/drm/vkms/vkms_drv.c  | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
index ac85e17428f8..09c012d54d58 100644
--- a/drivers/gpu/drm/vkms/vkms_crtc.c
+++ b/drivers/gpu/drm/vkms/vkms_crtc.c
@@ -86,6 +86,11 @@ static bool vkms_get_vblank_timestamp(struct drm_crtc *crtc,
 	struct vkms_output *output = &vkmsdev->output;
 	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
 
+	if (!READ_ONCE(vblank->enabled)) {
+		*vblank_time = ktime_get();
+		return true;
+	}
+
 	*vblank_time = READ_ONCE(output->vblank_hrtimer.node.expires);
 
 	if (WARN_ON(*vblank_time == vblank->time))
diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
index 1e8b2169d834..c2c83a01d4a7 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.c
+++ b/drivers/gpu/drm/vkms/vkms_drv.c
@@ -76,10 +76,10 @@ static void vkms_atomic_commit_tail(struct drm_atomic_state *old_state)
 
 	drm_atomic_helper_commit_modeset_disables(dev, old_state);
 
-	drm_atomic_helper_commit_planes(dev, old_state, 0);
-
 	drm_atomic_helper_commit_modeset_enables(dev, old_state);
 
+	drm_atomic_helper_commit_planes(dev, old_state, 0);
+
 	drm_atomic_helper_fake_vblank(old_state);
 
 	drm_atomic_helper_commit_hw_done(old_state);
-- 
2.17.1