[Intel-gfx] [PATCH v4] 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.

v4: Parameter and debug message naming improvements.
    Fix for link parameter check (Ville)

v3: Remove cached old link parameters. Instead, disable
    fast link training feature when link parameters are
    set (Ville)

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

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 | 17 +++++++++++++++++
 drivers/gpu/drm/i915/intel_drv.h              |  1 +
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 31ba241..82504f0 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1677,6 +1677,12 @@ found:
 void intel_dp_set_link_params(struct intel_dp *intel_dp,
 			      const struct intel_crtc_state *pipe_config)
 {
+	if (intel_dp->link_rate != pipe_config->port_clock ||
+	    intel_dp->lane_count != pipe_config->lane_count) {
+		intel_dp->train_set_valid = false;
+		DRM_DEBUG_KMS("setting train set valid as false\n");
+	}
+
 	intel_dp->link_rate = pipe_config->port_clock;
 	intel_dp->lane_count = pipe_config->lane_count;
 }
@@ -3849,7 +3855,7 @@ 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..e46bad6 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -85,6 +85,23 @@ static bool
 intel_dp_reset_link_train(struct intel_dp *intel_dp,
 			uint8_t dp_train_pat)
 {
+	bool has_dpcd;
+	bool no_aux_handshake = false;
+
+	has_dpcd = intel_dp_get_dpcd(intel_dp);
+
+	if (has_dpcd) {
+		if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11) {
+			no_aux_handshake = (intel_dp->dpcd[DP_MAX_DOWNSPREAD] &
+					    DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
+		}
+	}
+
+	intel_dp->train_set_valid &= no_aux_handshake;
+
+	DRM_DEBUG_KMS("link training optimization: %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);
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 798463e..94041fd 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1239,6 +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