[Intel-gfx] [PATCH v2] 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.

v2: Deal with DDI as well by moving the check into
    intel_dp_sink_dpms() (Dhinakaran)

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
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, 18 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index aa75f55eeb61..59169a4dc9d3 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2505,6 +2505,21 @@ static void ironlake_edp_pll_off(struct intel_dp *intel_dp)
 	udelay(200);
 }
 
+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;
+}
+
 /* If the sink supports it, try to set the power state appropriately */
 void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
 {
@@ -2515,6 +2530,9 @@ void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
 		return;
 
 	if (mode != DRM_MODE_DPMS_ON) {
+		if (downstream_hpd_needs_d0(intel_dp))
+			return;
+
 		ret = drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
 					 DP_SET_POWER_D3);
 	} else {
-- 
2.13.6