[Intel-gfx] [PATCH] drm/i915: Improve DP downstream HPD handling

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

DP dongles may signal downstream HPD via short HPD pulses. Setting the
sink to DPMS off apparently kills the downstream HPD (at least on my
DP->VGA dongle), so skip the DPMS off for such dongles when we turn
off the port.

Cc: David Woodhouse <dwmw2 at infradead.org>
Cc: Imre Deak <imre.deak at intel.com>
Cc: Pablo <pablodebiase at nanalysis.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103472
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99114
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index aa75f55eeb61..6ecc1b532f15 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2673,6 +2673,21 @@ static void intel_dp_get_config(struct intel_encoder *encoder,
 	}
 }
 
+static bool downstream_hpd_needs_d0(struct intel_dp *intel_dp)
+{
+	/*
+	 * DPCD 1.2 should support BRANCH_DEVICE_CTRL, and thus
+	 * be capable of signalling downstream hpd with a long pulse.
+	 * Whether or not that means D3 is safe to use is not clear,
+	 * but let's assume so until proven otherwise.
+	 *
+	 * FIXME should really check all downstream ports...
+	 */
+	return intel_dp->dpcd[DP_DPCD_REV] == 0x11 &&
+		intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT &&
+		intel_dp->downstream_ports[0] & DP_DS_PORT_HPD;
+}
+
 static void intel_disable_dp(struct intel_encoder *encoder,
 			     const struct intel_crtc_state *old_crtc_state,
 			     const struct drm_connector_state *old_conn_state)
@@ -2686,7 +2701,8 @@ static void intel_disable_dp(struct intel_encoder *encoder,
 	 * ensure that we have vdd while we switch off the panel. */
 	intel_edp_panel_vdd_on(intel_dp);
 	intel_edp_backlight_off(old_conn_state);
-	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
+	if (!downstream_hpd_needs_d0(intel_dp))
+		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
 	intel_edp_panel_off(intel_dp);
 }
 
-- 
2.13.6