[Intel-gfx] [PATCH] drm/i915/hdcp: Avoid duplicate HDCP enables

Sean Paul sean at poorly.run
Wed May 20 19:47:44 UTC 2020

From: Sean Paul <seanpaul at chromium.org>

If userspace sets the CP property to DESIRED while it's already ENABLED,
the driver will try to re-enable HDCP. On some displays, this will
result in R0' mismatches. I'm guessing this is because the display is
still sending back Ri instead of re-authenticating.

At any rate, we can fix this inefficiency easily enough by just nooping
the DESIRED property set if HDCP is already ENABLED.

Signed-off-by: Sean Paul <seanpaul at chromium.org>

I suspect this is the actual root cause I was chasing with
"drm/i915/hdcp: Add additional R0' wait". I was able to reproduce the
R0` messages by marking HDCP desired while it was already enabled. This
_should_ work, but it seems like some displays handle it more graciously
than others.

 drivers/gpu/drm/i915/display/intel_hdcp.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
index 2cbc4619b4ce..f770fe0c5595 100644
--- a/drivers/gpu/drm/i915/display/intel_hdcp.c
+++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
@@ -2156,12 +2156,16 @@ void intel_hdcp_atomic_check(struct drm_connector *connector,
-	 * Nothing to do if the state didn't change, or HDCP was activated since
-	 * the last commit. And also no change in hdcp content type.
+	 * Nothing to do if content type is unchanged and one of:
+	 *  - state didn't change
+	 *  - HDCP was activated since the last commit
+	 *  - attempting to set to desired while already enabled
 	if (old_cp == new_cp ||
 		if (old_state->hdcp_content_type ==
Sean Paul, Software Engineer, Google / Chromium OS

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