drm/i915/dp: Add debugfs entries to force the link rate/lane count

Add connector debugfs entries to force the link rate/lane count to be
used by a link training afterwards. These settings will be clamped to
the supported, i.e. the source's and sink's common rate/lane count.

After forcing the link rate/lane count reset the link training
parameters and for a non-auto setting disable reducing the link
parameters via the fallback logic. The former one can be used after
testing link training failure scenarios - via debugfs entries added
later - to reset the reduced link parameters after the test.

v2:
- Add the entries from intel_dp_link_training.c (Jani)
- Rename the entries to i915_dp_set_link_rate/lane_count.
v3: (Ville)
- Rename the entries/struct fields to force_link_rate/lane_count.
- Lock connection_mutex only for the required intel_dp state.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240610164933.2947366-18-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_display_debugfs.c

@@ -24,6 +24,7 @@
 #include "intel_display_types.h"
 #include "intel_dmc.h"
 #include "intel_dp.h"
+#include "intel_dp_link_training.h"
 #include "intel_dp_mst.h"
 #include "intel_drrs.h"
 #include "intel_fbc.h"
@@ -1517,6 +1518,7 @@ void intel_connector_debugfs_add(struct intel_connector *connector)
 	intel_pps_connector_debugfs_add(connector);
 	intel_psr_connector_debugfs_add(connector);
 	intel_alpm_lobf_debugfs_add(connector);
+	intel_dp_link_training_debugfs_add(connector);
 
 	if (connector_type == DRM_MODE_CONNECTOR_DisplayPort ||
 	    connector_type == DRM_MODE_CONNECTOR_HDMIA ||

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1771,6 +1771,8 @@ struct intel_dp {
 		int max_lane_count;
 		/* Max rate for the current link */
 		int max_rate;
+		int force_lane_count;
+		int force_rate;
 		bool retrain_disabled;
 		/* Sequential link training failures after a passing LT */
 		int seq_train_failures;

drivers/gpu/drm/i915/display/intel_dp.c

@@ -347,7 +347,7 @@ int intel_dp_max_common_rate(struct intel_dp *intel_dp)
 	return intel_dp_common_rate(intel_dp, intel_dp->num_common_rates - 1);
 }
 
-static int intel_dp_max_source_lane_count(struct intel_digital_port *dig_port)
+int intel_dp_max_source_lane_count(struct intel_digital_port *dig_port)
 {
 	int vbt_max_lanes = intel_bios_dp_max_lane_count(dig_port->base.devdata);
 	int max_lanes = dig_port->max_lanes;
@@ -373,19 +373,39 @@ int intel_dp_max_common_lane_count(struct intel_dp *intel_dp)
 	return min3(source_max, sink_max, lane_max);
 }
 
+static int forced_lane_count(struct intel_dp *intel_dp)
+{
+	return clamp(intel_dp->link.force_lane_count, 1, intel_dp_max_common_lane_count(intel_dp));
+}
+
 int intel_dp_max_lane_count(struct intel_dp *intel_dp)
 {
-	switch (intel_dp->link.max_lane_count) {
+	int lane_count;
+
+	if (intel_dp->link.force_lane_count)
+		lane_count = forced_lane_count(intel_dp);
+	else
+		lane_count = intel_dp->link.max_lane_count;
+
+	switch (lane_count) {
 	case 1:
 	case 2:
 	case 4:
-		return intel_dp->link.max_lane_count;
+		return lane_count;
 	default:
-		MISSING_CASE(intel_dp->link.max_lane_count);
+		MISSING_CASE(lane_count);
 		return 1;
 	}
 }
 
+static int intel_dp_min_lane_count(struct intel_dp *intel_dp)
+{
+	if (intel_dp->link.force_lane_count)
+		return forced_lane_count(intel_dp);
+
+	return 1;
+}
+
 /*
  * The required data bandwidth for a mode with given pixel clock and bpp. This
  * is the required net bandwidth independent of the data bandwidth efficiency.
@@ -1308,16 +1328,38 @@ static void intel_dp_print_rates(struct intel_dp *intel_dp)
 	drm_dbg_kms(&i915->drm, "common rates: %s\n", str);
 }
 
+static int forced_link_rate(struct intel_dp *intel_dp)
+{
+	int len = intel_dp_common_len_rate_limit(intel_dp, intel_dp->link.force_rate);
+
+	if (len == 0)
+		return intel_dp_common_rate(intel_dp, 0);
+
+	return intel_dp_common_rate(intel_dp, len - 1);
+}
+
 int
 intel_dp_max_link_rate(struct intel_dp *intel_dp)
 {
 	int len;
 
+	if (intel_dp->link.force_rate)
+		return forced_link_rate(intel_dp);
+
 	len = intel_dp_common_len_rate_limit(intel_dp, intel_dp->link.max_rate);
 
 	return intel_dp_common_rate(intel_dp, len - 1);
 }
 
+static int
+intel_dp_min_link_rate(struct intel_dp *intel_dp)
+{
+	if (intel_dp->link.force_rate)
+		return forced_link_rate(intel_dp);
+
+	return intel_dp_common_rate(intel_dp, 0);
+}
+
 int intel_dp_rate_select(struct intel_dp *intel_dp, int rate)
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
@@ -2287,13 +2329,14 @@ intel_dp_compute_config_limits(struct intel_dp *intel_dp,
 			       bool dsc,
 			       struct link_config_limits *limits)
 {
-	limits->min_rate = intel_dp_common_rate(intel_dp, 0);
+	limits->min_rate = intel_dp_min_link_rate(intel_dp);
 	limits->max_rate = intel_dp_max_link_rate(intel_dp);
 
 	/* FIXME 128b/132b SST support missing */
 	limits->max_rate = min(limits->max_rate, 810000);
+	limits->min_rate = min(limits->min_rate, limits->max_rate);
 
-	limits->min_lane_count = 1;
+	limits->min_lane_count = intel_dp_min_lane_count(intel_dp);
 	limits->max_lane_count = intel_dp_max_lane_count(intel_dp);
 
 	limits->pipe.min_bpp = intel_dp_min_bpp(crtc_state->output_format);
@@ -2962,7 +3005,7 @@ void intel_dp_set_link_params(struct intel_dp *intel_dp,
 	intel_dp->lane_count = lane_count;
 }
 
-static void intel_dp_reset_link_params(struct intel_dp *intel_dp)
+void intel_dp_reset_link_params(struct intel_dp *intel_dp)
 {
 	intel_dp->link.max_lane_count = intel_dp_max_common_lane_count(intel_dp);
 	intel_dp->link.max_rate = intel_dp_max_common_rate(intel_dp);

drivers/gpu/drm/i915/display/intel_dp.h

@@ -98,6 +98,7 @@ void intel_edp_backlight_off(const struct drm_connector_state *conn_state);
 void intel_edp_fixup_vbt_bpp(struct intel_encoder *encoder, int pipe_bpp);
 void intel_dp_mst_suspend(struct drm_i915_private *dev_priv);
 void intel_dp_mst_resume(struct drm_i915_private *dev_priv);
+int intel_dp_max_source_lane_count(struct intel_digital_port *dig_port);
 int intel_dp_max_link_rate(struct intel_dp *intel_dp);
 int intel_dp_max_lane_count(struct intel_dp *intel_dp);
 int intel_dp_config_required_rate(const struct intel_crtc_state *crtc_state);
@@ -107,6 +108,7 @@ int intel_dp_max_common_lane_count(struct intel_dp *intel_dp);
 int intel_dp_common_rate(struct intel_dp *intel_dp, int index);
 int intel_dp_rate_index(const int *rates, int len, int rate);
 void intel_dp_update_sink_caps(struct intel_dp *intel_dp);
+void intel_dp_reset_link_params(struct intel_dp *intel_dp);
 
 void intel_dp_compute_rate(struct intel_dp *intel_dp, int port_clock,
 			   u8 *link_bw, u8 *rate_select);

drivers/gpu/drm/i915/display/intel_dp_link_training.c

@@ -1115,6 +1115,9 @@ static int reduce_link_rate(struct intel_dp *intel_dp, int current_rate)
 	int rate_index;
 	int new_rate;
 
+	if (intel_dp->link.force_rate)
+		return -1;
+
 	rate_index = intel_dp_rate_index(intel_dp->common_rates,
 					 intel_dp->num_common_rates,
 					 current_rate);
@@ -1133,6 +1136,9 @@ static int reduce_link_rate(struct intel_dp *intel_dp, int current_rate)
 
 static int reduce_lane_count(struct intel_dp *intel_dp, int current_lane_count)
 {
+	if (intel_dp->link.force_lane_count)
+		return -1;
+
 	if (current_lane_count == 1)
 		return -1;
 
@@ -1555,3 +1561,226 @@ void intel_dp_128b132b_sdp_crc16(struct intel_dp *intel_dp,
 
 	lt_dbg(intel_dp, DP_PHY_DPRX, "DP2.0 SDP CRC16 for 128b/132b enabled\n");
 }
+
+static struct intel_dp *intel_connector_to_intel_dp(struct intel_connector *connector)
+{
+	if (connector->mst_port)
+		return connector->mst_port;
+	else
+		return enc_to_intel_dp(intel_attached_encoder(connector));
+}
+
+static int i915_dp_force_link_rate_show(struct seq_file *m, void *data)
+{
+	struct intel_connector *connector = to_intel_connector(m->private);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = intel_connector_to_intel_dp(connector);
+	int current_rate = -1;
+	int force_rate;
+	int err;
+	int i;
+
+	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
+	if (err)
+		return err;
+
+	if (intel_dp->link_trained)
+		current_rate = intel_dp->link_rate;
+	force_rate = intel_dp->link.force_rate;
+
+	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
+
+	seq_printf(m, "%sauto%s",
+		   force_rate == 0 ? "[" : "",
+		   force_rate == 0 ? "]" : "");
+
+	for (i = 0; i < intel_dp->num_source_rates; i++)
+		seq_printf(m, " %s%d%s%s",
+			   intel_dp->source_rates[i] == force_rate ? "[" : "",
+			   intel_dp->source_rates[i],
+			   intel_dp->source_rates[i] == current_rate ? "*" : "",
+			   intel_dp->source_rates[i] == force_rate ? "]" : "");
+
+	seq_putc(m, '\n');
+
+	return 0;
+}
+
+static int parse_link_rate(struct intel_dp *intel_dp, const char __user *ubuf, size_t len)
+{
+	char *kbuf;
+	const char *p;
+	int rate;
+	int ret = 0;
+
+	kbuf = memdup_user_nul(ubuf, len);
+	if (IS_ERR(kbuf))
+		return PTR_ERR(kbuf);
+
+	p = strim(kbuf);
+
+	if (!strcmp(p, "auto")) {
+		rate = 0;
+	} else {
+		ret = kstrtoint(p, 0, &rate);
+		if (ret < 0)
+			goto out_free;
+
+		if (intel_dp_rate_index(intel_dp->source_rates,
+					intel_dp->num_source_rates,
+					rate) < 0)
+			ret = -EINVAL;
+	}
+
+out_free:
+	kfree(kbuf);
+
+	return ret < 0 ? ret : rate;
+}
+
+static ssize_t i915_dp_force_link_rate_write(struct file *file,
+					     const char __user *ubuf,
+					     size_t len, loff_t *offp)
+{
+	struct seq_file *m = file->private_data;
+	struct intel_connector *connector = to_intel_connector(m->private);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = intel_connector_to_intel_dp(connector);
+	int rate;
+	int err;
+
+	rate = parse_link_rate(intel_dp, ubuf, len);
+	if (rate < 0)
+		return rate;
+
+	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
+	if (err)
+		return err;
+
+	intel_dp_reset_link_params(intel_dp);
+	intel_dp->link.force_rate = rate;
+
+	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
+
+	*offp += len;
+
+	return len;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(i915_dp_force_link_rate);
+
+static int i915_dp_force_lane_count_show(struct seq_file *m, void *data)
+{
+	struct intel_connector *connector = to_intel_connector(m->private);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = intel_connector_to_intel_dp(connector);
+	int current_lane_count = -1;
+	int force_lane_count;
+	int err;
+	int i;
+
+	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
+	if (err)
+		return err;
+
+	if (intel_dp->link_trained)
+		current_lane_count = intel_dp->lane_count;
+	force_lane_count = intel_dp->link.force_lane_count;
+
+	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
+
+	seq_printf(m, "%sauto%s",
+		   force_lane_count == 0 ? "[" : "",
+		   force_lane_count == 0 ? "]" : "");
+
+	for (i = 1; i <= 4; i <<= 1)
+		seq_printf(m, " %s%d%s%s",
+			   i == force_lane_count ? "[" : "",
+			   i,
+			   i == current_lane_count ? "*" : "",
+			   i == force_lane_count ? "]" : "");
+
+	seq_putc(m, '\n');
+
+	return 0;
+}
+
+static int parse_lane_count(const char __user *ubuf, size_t len)
+{
+	char *kbuf;
+	const char *p;
+	int lane_count;
+	int ret = 0;
+
+	kbuf = memdup_user_nul(ubuf, len);
+	if (IS_ERR(kbuf))
+		return PTR_ERR(kbuf);
+
+	p = strim(kbuf);
+
+	if (!strcmp(p, "auto")) {
+		lane_count = 0;
+	} else {
+		ret = kstrtoint(p, 0, &lane_count);
+		if (ret < 0)
+			goto out_free;
+
+		switch (lane_count) {
+		case 1:
+		case 2:
+		case 4:
+			break;
+		default:
+			ret = -EINVAL;
+		}
+	}
+
+out_free:
+	kfree(kbuf);
+
+	return ret < 0 ? ret : lane_count;
+}
+
+static ssize_t i915_dp_force_lane_count_write(struct file *file,
+					      const char __user *ubuf,
+					      size_t len, loff_t *offp)
+{
+	struct seq_file *m = file->private_data;
+	struct intel_connector *connector = to_intel_connector(m->private);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = intel_connector_to_intel_dp(connector);
+	int lane_count;
+	int err;
+
+	lane_count = parse_lane_count(ubuf, len);
+	if (lane_count < 0)
+		return lane_count;
+
+	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
+	if (err)
+		return err;
+
+	intel_dp_reset_link_params(intel_dp);
+	intel_dp->link.force_lane_count = lane_count;
+
+	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
+
+	*offp += len;
+
+	return len;
+}
+DEFINE_SHOW_STORE_ATTRIBUTE(i915_dp_force_lane_count);
+
+void intel_dp_link_training_debugfs_add(struct intel_connector *connector)
+{
+	struct dentry *root = connector->base.debugfs_entry;
+
+	if (connector->base.connector_type != DRM_MODE_CONNECTOR_DisplayPort &&
+	    connector->base.connector_type != DRM_MODE_CONNECTOR_eDP)
+		return;
+
+	debugfs_create_file("i915_dp_force_link_rate", 0644, root,
+			    connector, &i915_dp_force_link_rate_fops);
+
+	debugfs_create_file("i915_dp_force_lane_count", 0644, root,
+			    connector, &i915_dp_force_lane_count_fops);
+}

drivers/gpu/drm/i915/display/intel_dp_link_training.h

@@ -9,6 +9,7 @@
 #include <drm/display/drm_dp_helper.h>
 
 struct intel_atomic_state;
+struct intel_connector;
 struct intel_crtc_state;
 struct intel_dp;
 
@@ -44,4 +45,7 @@ static inline u8 intel_dp_training_pattern_symbol(u8 pattern)
 
 void intel_dp_128b132b_sdp_crc16(struct intel_dp *intel_dp,
 				 const struct intel_crtc_state *crtc_state);
+
+void intel_dp_link_training_debugfs_add(struct intel_connector *connector);
+
 #endif /* __INTEL_DP_LINK_TRAINING_H__ */