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

1 files changed, 229 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
index af6536936550..8a2ebee7a842 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/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);
+}