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Subject[PATCH 5.4 258/320] drm/bridge: analogix_dp: Make PSR-exit block less
From: Brian Norris <>

commit c4c6ef229593366ab593d4d424addc7025b54a76 upstream.

Prior to commit 6c836d965bad ("drm/rockchip: Use the helpers for PSR"),
"PSR exit" used non-blocking analogix_dp_send_psr_spd(). The refactor
started using the blocking variant, for a variety of reasons -- quoting
Sean Paul's potentially-faulty memory:

- To avoid racing a subsequent PSR entry (if exit takes a long time)
- To avoid racing disable/modeset
- We're not displaying new content while exiting PSR anyways, so there
is minimal utility in allowing frames to be submitted
- We're lying to userspace telling them frames are on the screen when
we're just dropping them on the floor

However, I'm finding that this blocking transition is causing upwards of
60+ ms of unneeded latency on PSR-exit, to the point that initial cursor
movements when leaving PSR are unbearably jumpy.

It turns out that we need to meet in the middle somewhere: Sean is right
that we were "lying to userspace" with a non-blocking PSR-exit, but the
new blocking behavior is also waiting too long:

According to the eDP specification, the sink device must support PSR
entry transitions from both state 4 (ACTIVE_RESYNC) and state 0
(INACTIVE). It also states that in ACTIVE_RESYNC, "the Sink device must
display the incoming active frames from the Source device with no
visible glitches and/or artifacts."

Thus, for our purposes, we only need to wait for ACTIVE_RESYNC before
moving on; we are ready to display video, and subsequent PSR-entry is

Tested on a Samsung Chromebook Plus (i.e., Rockchip RK3399 Gru Kevin),
where this saves about 60ms of latency, for PSR-exit that used to
take about 80ms.

Fixes: 6c836d965bad ("drm/rockchip: Use the helpers for PSR")
Cc: <>
Cc: Zain Wang <>
Cc: Tomasz Figa <>
Cc: Heiko Stuebner <>
Cc: Sean Paul <>
Signed-off-by: Brian Norris <>
Reviewed-by: Sean Paul <>
Signed-off-by: Robert Foss <>
Signed-off-by: Greg Kroah-Hartman <>
drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
@@ -1086,11 +1086,21 @@ int analogix_dp_send_psr_spd(struct anal
if (!blocking)
return 0;

+ /*
+ * db[1]!=0: entering PSR, wait for fully active remote frame buffer.
+ * db[1]==0: exiting PSR, wait for either
+ * (a) ACTIVE_RESYNC - the sink "must display the
+ * incoming active frames from the Source device with no visible
+ * glitches and/or artifacts", even though timings may still be
+ * re-synchronizing; or
+ * (b) INACTIVE - the transition is fully complete.
+ */
ret = readx_poll_timeout(analogix_dp_get_psr_status, dp, psr_status,
psr_status >= 0 &&
((vsc->db[1] && psr_status == DP_PSR_SINK_ACTIVE_RFB) ||
- (!vsc->db[1] && psr_status == DP_PSR_SINK_INACTIVE)), 1500,
+ (!vsc->db[1] && (psr_status == DP_PSR_SINK_ACTIVE_RESYNC ||
+ psr_status == DP_PSR_SINK_INACTIVE))),
+ 1500, DP_TIMEOUT_PSR_LOOP_MS * 1000);
if (ret) {
dev_warn(dp->dev, "Failed to apply PSR %d\n", ret);
return ret;

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