[PATCH 2/2] drm/atomic: Force bridge self-refresh-exit on CRTC switch

[Brian Norris]

It's possible to change which CRTC is in use for a given
connector/encoder/bridge while we're in self-refresh without fully
disabling the connector/encoder/bridge along the way. This can confuse
the bridge encoder/bridge, because
(a) it needs to track the SR state (trying to perform "active"
    operations while the panel is still in SR can be Bad(TM)); and
(b) it tracks the SR state via the CRTC state (and after the switch, the
    previous SR state is lost).

Thus, we need to either somehow carry the self-refresh state over to the
new CRTC, or else force an encoder/bridge self-refresh transition during
such a switch.

I choose the latter, so we disable the encoder (and exit PSR) before
attaching it to the new CRTC (where we can continue to assume a clean
(non-self-refresh) state).

This fixes PSR issues seen on Rockchip RK3399 systems with
drivers/gpu/drm/bridge/analogix/analogix_dp_core.c.

Cc: <stable at vger.kernel.org>
Fixes: 1452c25b0e60 ("drm: Add helpers to kick off self refresh mode in drivers")
Signed-off-by: Brian Norris <briannorris at chromium.org>
---

 drivers/gpu/drm/drm_atomic_helper.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 9603193d2fa1..74161d007894 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1011,9 +1011,19 @@ crtc_needs_disable(struct drm_crtc_state *old_state,
 		return drm_atomic_crtc_effectively_active(old_state);
 
 	/*
-	 * We need to run through the crtc_funcs->disable() function if the CRTC
-	 * is currently on, if it's transitioning to self refresh mode, or if
-	 * it's in self refresh mode and needs to be fully disabled.
+	 * We need to disable bridge(s) and CRTC if we're transitioning out of
+	 * self-refresh and changing CRTCs at the same time, because the
+	 * bridge tracks self-refresh status via CRTC state.
+	 */
+	if (old_state->self_refresh_active && new_state->enable &&
+	    old_state->crtc != new_state->crtc)
+		return true;
+
+	/*
+	 * We also need to run through the crtc_funcs->disable() function if
+	 * the CRTC is currently on, if it's transitioning to self refresh
+	 * mode, or if it's in self refresh mode and needs to be fully
+	 * disabled.
 	 */
 	return old_state->active ||
 	       (old_state->self_refresh_active && !new_state->active) ||
-- 
2.35.1.265.g69c8d7142f-goog