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[v3,12/13] drm/sun4i: backend: Make sure we don't have a commit pending

Message ID f6a37c66a827518a423fdbdfd45dc6065cdc2af0.1515492513.git-series.maxime.ripard@free-electrons.com
State Accepted
Commit dd63250c55bf26a814c957f6772e8f8683b70077
Headers show
Series [v3,01/13] drm/sun4i: backend: Move line stride setup to buffer setup function | expand

Commit Message

Maxime Ripard Jan. 9, 2018, 10:09 a.m. UTC 
If we try to read the backend registers while it fetches the new values, we
end up with the value of some random register instead of the one we asked
for.

In order to prevent that, let's make sure that the very first thing we do
during our atomic modesetting is to let the commit bit come to a rest.

We don't have to worry about anything else since the only time we will
trigger a new transaction is during the atomic_commit which comes much
later.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/gpu/drm/sun4i/sun4i_backend.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)
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Patch

diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c
index 4642f933765e..a18c86a15748 100644
--- a/drivers/gpu/drm/sun4i/sun4i_backend.c
+++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
@@ -297,6 +297,17 @@  static bool sun4i_backend_plane_uses_frontend(struct drm_plane_state *state)
 	return sun4i_backend_plane_uses_scaler(state);
 }
 
+static void sun4i_backend_atomic_begin(struct sunxi_engine *engine,
+				       struct drm_crtc_state *old_state)
+{
+	u32 val;
+
+	WARN_ON(regmap_read_poll_timeout(engine->regs,
+					 SUN4I_BACKEND_REGBUFFCTL_REG,
+					 val, !(val & SUN4I_BACKEND_REGBUFFCTL_LOADCTL),
+					 100, 50000));
+}
+
 static int sun4i_backend_atomic_check(struct sunxi_engine *engine,
 				      struct drm_crtc_state *crtc_state)
 {
@@ -478,6 +489,7 @@  static struct sun4i_frontend *sun4i_backend_find_frontend(struct sun4i_drv *drv,
 }
 
 static const struct sunxi_engine_ops sun4i_backend_engine_ops = {
+	.atomic_begin			= sun4i_backend_atomic_begin,
 	.atomic_check			= sun4i_backend_atomic_check,
 	.commit				= sun4i_backend_commit,
 	.layers_init			= sun4i_layers_init,