[PATCH] drm/i915/dp: Send DPCD ON for MST before phy_up

[Lyude Paul <lyude@redhat.com>]

As it turns out, the aux block being off was not the real problem here,
as transition from D3 to D0 is mandated by the DP spec to take a maximum
of 1ms, whereas we're allowed a 100ms timeframe to respond to ESI irqs.
The real problem here is a bit more subtle.

When doing a modeset where the problem of the sink timing out to our
sideband requests when transitioning from D3 to D0 occurs, the timeout
is from the aux block not coming on. However, nothing else times out
other than the initial phy_up message because the DPCD on call in
intel_ddi_enable_dp() ends up waking up the AUX block on the hub, not
the phy_up sideband message. This means that the real fix we need is to
use the DPMS on before sending a phy_up to ensure that the hub is ready
to accept sideband messages.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: stable@vger.kernel.org
Fixes: ad260ab32a4d9 ("drm/i915/dp: Write to SET_POWER dpcd to enable MST hub.")
---
 drivers/gpu/drm/i915/intel_ddi.c    | 6 +++++-
 drivers/gpu/drm/i915/intel_dp_mst.c | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index a6672a9abd85..9bd675f73f7b 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -2324,7 +2324,11 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
 		intel_prepare_dp_ddi_buffers(encoder, crtc_state);
 
 	intel_ddi_init_dp_buf_reg(encoder);
-	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
+	/* for MST, we do DPMS_ON outside of here so that DPMS_ON can happen
+	 * before drm_dp_send_power_updown_phy()
+	 */
+	if (!intel_dp->is_mst)
+		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
 	intel_dp_start_link_train(intel_dp);
 	if (port != PORT_A || INTEL_GEN(dev_priv) >= 9)
 		intel_dp_stop_link_train(intel_dp);
diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index c3de0918ee13..eff9a4eae1f0 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -223,6 +223,7 @@ static void intel_mst_pre_enable_dp(struct intel_encoder *encoder,
 
 	DRM_DEBUG_KMS("active links %d\n", intel_dp->active_mst_links);
 
+	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
 	drm_dp_send_power_updown_phy(&intel_dp->mst_mgr, connector->port, true);
 	if (intel_dp->active_mst_links == 0)
 		intel_dig_port->base.pre_enable(&intel_dig_port->base,
-- 
2.14.3