[Intel-gfx] [PATCH v2] drm/i915: Disable fast link training if DP config changes

[Mika Kahola]

Disable DP fast link training if DP link configuration
changes. If one of the DP link parameters i.e. link
bandwidth, lane count, rate selection, port clock or bpp
changes the link training does no longer apply the
previously computed voltage swing and pre-emphasis values.
Instead, the link training is started with zero values.

v2:
Readout DPCD register to check if no aux handshaking is
required in link training (Ander)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91393
Signed-off-by: Mika Kahola <mika.kahola at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c               |  8 +++++-
 drivers/gpu/drm/i915/intel_dp_link_training.c | 39 +++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_drv.h              |  7 ++++-
 3 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index f2bfca0..a15e617 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1621,6 +1621,12 @@ found:
 	intel_dp_compute_rate(intel_dp, pipe_config->port_clock,
 			      &link_bw, &rate_select);
 
+	intel_dp->link_bw = link_bw;
+	intel_dp->rate_select = rate_select;
+	intel_dp->lane_count = lane_count;
+	intel_dp->port_clock = pipe_config->port_clock;
+	intel_dp->bpp = bpp;
+
 	DRM_DEBUG_KMS("DP link bw %02x rate select %02x lane count %d clock %d bpp %d\n",
 		      link_bw, rate_select, pipe_config->lane_count,
 		      pipe_config->port_clock, bpp);
@@ -3828,7 +3834,7 @@ intel_dp_link_down(struct intel_dp *intel_dp)
 	intel_dp->DP = DP;
 }
 
-static bool
+bool
 intel_dp_get_dpcd(struct intel_dp *intel_dp)
 {
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index 8888793..1e7f92a 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -82,9 +82,43 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
 }
 
 static bool
+intel_dp_check_conf(struct intel_dp *intel_dp)
+{
+	if (intel_dp->link_bw != intel_dp->old_link_bw)
+		return false;
+	else if (intel_dp->lane_count != intel_dp->old_lane_count)
+		return false;
+	else if (intel_dp->rate_select != intel_dp->old_rate_select)
+		return false;
+	else if (intel_dp->port_clock != intel_dp->old_port_clock)
+		return false;
+	else if (intel_dp->bpp != intel_dp->old_bpp)
+		return false;
+	else
+		return true;
+}
+
+static bool
 intel_dp_reset_link_train(struct intel_dp *intel_dp,
 			uint8_t dp_train_pat)
 {
+	bool has_dpcd;
+	bool flt_supported = false;
+
+	has_dpcd = intel_dp_get_dpcd(intel_dp);
+
+	if (has_dpcd) {
+		if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11)
+			flt_supported = (intel_dp->dpcd[DP_MAX_DOWNSPREAD] &
+					 DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
+	}
+
+	intel_dp->train_set_valid &= flt_supported;
+	intel_dp->train_set_valid &= intel_dp_check_conf(intel_dp);
+
+	DRM_DEBUG_KMS("fast link training enabled: %s\n",
+		      intel_dp->train_set_valid ? "true" : "false");
+
 	if (!intel_dp->train_set_valid)
 		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
 	intel_dp_set_signal_levels(intel_dp);
@@ -305,6 +339,11 @@ intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
 
 	if (channel_eq) {
 		intel_dp->train_set_valid = true;
+		intel_dp->old_link_bw = intel_dp->link_bw;
+		intel_dp->old_rate_select = intel_dp->rate_select;
+		intel_dp->old_lane_count = intel_dp->lane_count;
+		intel_dp->old_port_clock = intel_dp->port_clock;
+		intel_dp->old_bpp = intel_dp->bpp;
 		DRM_DEBUG_KMS("Channel EQ done. DP Training successful\n");
 	}
 }
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 1ffd8d5..3d8c8dd 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -745,7 +745,11 @@ struct intel_dp {
 	i915_reg_t aux_ch_data_reg[5];
 	uint32_t DP;
 	int link_rate;
-	uint8_t lane_count;
+	uint8_t lane_count, old_lane_count;
+	uint8_t link_bw, old_link_bw;
+	uint8_t rate_select, old_rate_select;
+	int port_clock, old_port_clock;
+	int bpp, old_bpp;
 	bool has_audio;
 	enum hdmi_force_audio force_audio;
 	bool limited_color_range;
@@ -1235,6 +1239,7 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc);
 bool intel_dp_compute_config(struct intel_encoder *encoder,
 			     struct intel_crtc_state *pipe_config);
 bool intel_dp_is_edp(struct drm_device *dev, enum port port);
+bool intel_dp_get_dpcd(struct intel_dp *intel_dp);
 enum irqreturn intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port,
 				  bool long_hpd);
 void intel_edp_backlight_on(struct intel_dp *intel_dp);
-- 
1.9.1